Colored articles and compositions and methods for their fabrication

ABSTRACT

This invention provides improved methods and compositions for achieving material coloration using particle scattering. These coloration effects can be designed to be either highly stable or dependent upon the switching effects of either temperature, integrated thermal exposure, moisture absorption, or exposure to actinic radiation. Articles employing materials with these coloration effects are described. Composition comprise a solid, light-transmitting matrix component having a non-liquid particle scattering colorant dispersed. Articles are produced wherein another solid second matrix component has an electronic transition colorant dispersed therein and the first and second compositions are disposed on one another, and optionally interpenetrate each other. Colored articles are produced in the form of fibers, films and molded articles.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is a division of U.S. patent application Ser.No. 09/758,534, filed Jan. 10, 2001, which is a division of U.S. patentapplication Ser. No. 08/535,687, filed Sep. 28, 1995, now U.S. Pat. No.5,932,309, the entire disclosures of which are hereby incorporated byreference.

BACKGROUND OF THE INVENTION

[0002] This invention relates to improved methods and compositions forthe achievement of material coloration using particle scattering, aswell as articles employing these material colorations.

[0003] In the prior art it is well known to color materials using dyesand pigments. Unfortunately, pigment and dye coloration agents sufferfading effects due to exposure to ultraviolet light, ozone or bleach.The usual cause of this fading is chemical changes in the colorant.These chemical changes alter the electronic transitions of the colorant,thereby causing undesired instability in color. For example,anthraquinone-based blue dyes fade upon exposure to ozone. Since mostdyes contain a blue component, blue-fading causes fading in virtuallyevery color.

[0004] It is very common in commerce to color polymers, however, coloredpolymer, such as dyed polymers are also difficult to recycle. Mosthigh-value end-use applications require the separation of recycledplastics by color. However, due to the many colors available, separationby color is rarely done. Instead, most recycling companies separateplastics into a colorless lot and a mixed-color lot. Since dye removalis energy intensive, costly, and causes waste disposal problems for thespent dye, colored plastics remain in the mixed-color lot. Recycledpolymer from this lot produces a marbled polymer or, at best, anoff-green or brown polymer which has limited usefulness. Due to thesedifficulties, many recycling facilities do not even collect coloredplastics. Those that do accept colored plastics often incinerate themixed-color lot. Unfortunately, in some applications, such as carpets,almost all of the material available for recycling is colored. As aresult, these polymers are rarely recycled. Consequently, billions ofpounds of used carpets are discarded in landfills each year, therebywasting valuable natural resources.

[0005] The use of chemical colorants, such as pigments or dyes, alsopotentially poses problems related to pigment toxicity and waste streammanagement. Many pigments contain toxic, heavy metals. A wet-dyeingprocess produces spent-dye baths. This dye-house effluent can have anegative environmental impact. The range of achievable optical effectsis also restricted if the only colorants are dyes and pigments. A newtechnology is needed which will address fading, recyclability, dye-houseeffluent, and toxicity.

[0006] It would be advantageous to provide improved methods ofcoloration that provide switchability from one color state to another.Such color changing compositions can be used, for example, for cosmeticpurposes in polymer fibers used for textiles and carpets and forcolor-changing windows and displays. Additionally, this type oftechnology could be used in military applications for camouflageclothing, tents, and machinery. If such color change is reversiblyswitched as a consequence of light exposure, temperature changes, orhumidity changes, then chameleon effects can be achieved for sucharticles. If the color switching effect is a one-time event caused byactinic radiation or high temperature exposure, the switching effect canbe used to provide spatially dependent coloration.

[0007] Enhancing the value of polymer films, fibers, coatings, and otherarticles by achieving novel optical effects provides a major commercialgoal. One advance in this area is described in U.S. Pat. No. 5,233,465which provides a polymer film having metallic luster resulting from themultiple layering of colorless polymers having differing refractiveindices. These films and derived fibers are presently used for cosmeticpurposes in many applications, such as for product packaging and textilearticles. Another advance is provided by the formation of aparallel-line relief pattern on the surface of a polymer film. This alsoresults in chromatic effects without the use of dyes or pigments. Atechnology of this type in which the parallel-lines relief patternconsists of prisms is described in U.S. Pat. No. 4,805,984. Such polymerfilms are available commercially for solar window and light conduitapplications.

[0008] The embossing of polymer films, especially metallized polymerfilms, to achieve novel optical effects is also well known. U.S. Pat.No. 4,886,687 describes non-pigmented coloration as a result ofdiffraction effects originating from an embossed pattern having 5,000 to100,000 lines per inch (corresponding to a periodicity of about 0.25 to5 microns) . While such embossing provides striking visual effects foreither films or film strips, such effects are difficult to perceive forpolymer fibers having small diameters and conventional fibercross-sections. Also, the embossing described in U.S. Pat. No. 4,886,687is described to be preferably holographically generated by theinterference of two coherent light beams. While such an embossing methodcan provide high reliability of the fidelity of the embossing process,it is also quite expensive.

[0009] Novel optical effects in silicate glasses have been achievedusing colloidal particles of metals. U.S. Pat. No. 4,017,318 describesglass articles that, after exposure to actinic radiations, can be heattreated to provide coloration effects because of colloidal silverparticles. U.S. Pat. Nos. 2,515,936; 2,515,943 and 2,651,145 alsodescribe methods of generating colored silicate glasses usingcombinations of various colloidal metals, including colloidal gold andsilver. Pearlescent compositions are also widely used to provide noveloptical effects, including color, to polymer articles. Thesecompositions, such as described in U.S. Pat. Nos. 3,087,829 and4,146,403, provide coloration due to the interference of light reflectedfrom parallel opposite sides of platelets deposited on the plate sidesof mica substrate particles. This interference-derived colorationprocess critically depends upon the nearly perfect parallel arrangementof the reflecting surfaces of plates. Hence, such colorants aresometimes referred to as plate interference colorants. Due to the manymicron diameter of the plates, such particles are unsuitable for thespinning of fibers of the types conventionally used for textiles andcarpets, since the available pearlescent platelets have lateraldimensions that are comparable to the diameter of the such fibers. As aresult, these platelets are either filtered out during the fiberspinning process or they clog spinneret holes. The pearlescent plateletsare preferably aligned parallel to the polymer surface. Without suchparallel alignment, the color effect is not as dramatic. Additionally,thick polymer articles are required in order for the iridescence to bepronounced at the loading levels that can be used without severelydegrading polymer mechanical properties.

[0010] Christiansen filters have been known for over a century. Suchfilters usually consist of particles of a solid in a liquid matrix. Theparticles and the host matrix are chosen so that the wavelengthdependence of the refractive index of the host matrix and particles aresubstantially different and there exist a wavelength at which therefractive index of the host matrix and the particles are equal. At thatwavelength the filter is transmissive and at wavelengths remote fromthat wavelength the light is largely scattered and not transmitted. Foreffective operation at visible wavelengths, such filters should notcontain components that significantly absorb light at these wavelengths.U.S. Pat. No. 3,586,417 shows that the wavelength at which aChristiansen filter transmits can be varied for an optical device byvarying the temperature of the filter. Such variation results from thedifferent temperature coefficients for the refractive indices of thescattering particles and the liquid matrix. Various new methods forproducing Christiansen filters, including some efforts to makesolid-matrix optical devices, are described by Balasubramanian, AppliedOptics 31, pp. 1574-1587 (1992). While Christiansen filters are veryuseful for providing wavelength-selective light transmission for opticalapplications, means for obtaining specially enhanced coloration effectsfor scattered light using the Christiansen effect have not beenpreviously demonstrated. Such enhanced effects for scattered light havecritical importance for the development of new technologies forachieving material coloration.

[0011] The present invention eliminates the above described problems ofprior art technologies by the use of coloration associated with particlescattering. Materials and methods for modifying and enhancing thecoloration effects of particle scattering are provided by thisinvention.

SUMMARY OF THE INVENTION

[0012] The invention provides a composite article comprising a firstcomposition and a second composition. The first composition comprises asolid first matrix component having a non-liquid particle scatteringcolorant dispersed therein, and the second composition comprises a solidsecond matrix component having an electronic transition colorant, dye orpigment dispersed therein. The first composition is either disposed onand substantially exterior to the second composition on at least oneside of the article or the first and second compositions aresubstantially mutually interpenetrating. There exists at least oneincident visible light wavelength and one light angle such that thefirst composition absorbs less than about 90% of the light incident onthe article. The absorption coefficient of the first composition is lessthan about 50% of that of the second composition at a wavelength in thevisible region of the spectrum. The particle scattering colorant doesnot have a highest peak in absorption coefficient that falls in thevisible region of the spectrum. Either (a) the particle scatteringcolorant has a refractive index that matches that of the first matrixcomponent at a wavelength in the visible and has an average particlesize of less than about 2000 microns or (b) the average refractive indexof the particle scattering colorant differs from that of the firstmatrix component by at least about 5% in the visible wavelength range,the average particle size of the particle scattering colorant in thesmallest dimension is less than about 2 microns, and the particlescattering colorant, when dispersed in a colorless, isotropic liquidhaving a substantially different refractive index, is characterized atvisible wavelengths as having an effective maximum absorbance that is atleast about 2 times the effective minimum absorbance.

[0013] The invention also provides a fiber comprising a polymer matrixcomponent in which particle scattering colorant particles are dispersed.The particle scattering colorant comprises either a semiconductor, ametallic conductor, a metal oxide or a salt. The particle scatteringcolorant has an average diameter in the smallest dimension of less thanabout 2 microns. The particle scattering colorant has a minimum in thetransmitted light intensity ratio in the 380 to 750 nm range that isshifted at least by 10 nm compared with that obtained for the samesemiconductor, metallic conductor, metal oxide or salt, having anaverage particle size above about 20 microns.

[0014] The invention further provides a composite article in fiber formcomprising a polymer matrix having dispersed therein particles selectedfrom the group consisting of ferroelectric, antiferroelectric andphotoferroelectric particles. The invention also provides processes forproducing composite articles.

[0015] The invention still further provides a polymer compositioncomprising in admixture, a polymer matrix, at least one particlescattering colorant, and at least one electronic transition colorant,dye or pigment wherein (a) either the refractive index differencebetween the polymer matrix and the particle scattering colorant or theabsorption spectra of the electronic transition colorant, dye or pigmentundergoes substantial change as a result of one or more of a temperaturechange, humidity change, an electric field change, pressure change,exposure to a chemical agent, integrated thermal exposure, or exposureto either light or actinic radiation and (b) states exist in whicheither the average refractive index of the particle scattering colorantand the polymer matrix differ by at least 5% in the entire visiblespectral region or the refractive index of the particle scatteringcolorant and the polymer matrix are matched at a wavelength in thevisible spectra region.

[0016] The invention also provides an article in the form of a film,fiber, or molded part comprising a particle scattering colorantdispersed in a polymer matrix, wherein the average particle size of theparticle scattering colorant in its smallest dimension is less thanabout 2 microns and wherein either (a) the particle scattering coloranthas a coating thereon and the refractive index of the coating differsfrom that of the polymer matrix by at least 10% at all wavelengths inthe visible region of the spectrum or (b) the particle scatteringcolorant is comprised of a series of layers that differ in refractiveindices between adjacent layers by at least 5%.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0017] The invention provides improved methods and compositions forcoloring materials using light scattering by particles that aredispersed within matrices which are at least partially lighttransmissive.

[0018] The colorants useful for this invention are called particlescattering colorants. Such colorants are distinguished from colorantsthat provide coloration due to the interference between light reflectedfrom opposite parallel sides or interfaces of plate-like particles,called plate-like interference colorants, and those that providecoloration due to electronic transitions, called electronic transitioncolorants. While particle scattering colorants can provide a degree ofcoloration by electronic transitions, a colorant is a particlescattering colorant for the purpose of this invention only if colorationdepends on the size of the particles and there is no significantcoloration from the interference of light reflected from opposite sidesor interfaces of parallel plates. Plate-like interference colorants arespecifically excluded from the definition of particle scatteringcolorants. A plate-like interference colorant is a flat layered materialcomprising a flat plate layer having a thickness that is between 50 and1000 nm.

[0019] In order for a material to be a particle scattering colorant, itmust satisfy certain requirements that depend on the inventionembodiment. Particle scattering colorants are either absorbing particlescattering colorants or non-absorbing particle scattering colorantsdepending on whether or not the particle scattering colorantssignificantly absorb light in the visible region of the spectrum.Absorption is evidenced by the visual perception of color when particlesizes are sufficiently large that particle scattering of light is notsignificant.

[0020] For invention embodiments of a first category, a particlecolorant is used by dispersing it in a solid matrix that has asubstantially different refractive index in the visible than that of theparticle scattering colorant. For this first category, a particlescattering colorant is defined as a material that has either the A or Bproperty as defined below.

[0021] The A or B properties are determined by dispersing the candidateparticle scattering colorant in a colorless isotropic liquid that has arefractive index that is as different from that of the candidateparticle scattering colorant as is conveniently obtainable. The mostreliable test will result from choosing the refractive index differenceof the liquid and the candidate particle scattering colorant to be aslarge as possible. This liquid-solid mixture containing only thecandidate particle scattering colorant and the colorless isotropicliquid is referred to as the particle test mixture. The negativelogarithmic ratio of transmitted light intensity to incident lightintensity (−log (l/l_(o))) is measured for the particle test mixture asa continuous function of wavelength over a wavelength range thatincludes the entire visible spectral region from 380 to 750 nm. Suchmeasurements, can be conveniently accomplished using an ordinaryUV-visible spectrometer. The obtained quantity (−log(l/l_(o)) is calledthe effective absorbance, since it includes the effects of bothscattering and absorption on reducing the intensity of transmittedlight.

[0022] The A property is only a valid determinant for particlescattering colorants for materials which do not significantly absorb inthe visible region of the spectrum, which means that absorption is notso large as to overwhelm the coloration effects due to particlescattering. For the sole purpose of the A property test, a material thatdoes not significantly absorb in the visible region is defined as onewhose particle test mixture has an effective maximum absorbance in thespectral region of from about 380 to about 750 nm that decreases by atleast about 2 times and preferably at least about 3 times when theaverage particle size of the candidate particle scattering colorant isincreased to above about 20 microns without changing the gravimetricconcentration of the candidate particle scattering colorant in theparticle test mixture.

[0023] It should be understood that the above described ratios ofabsorbances will in general have a weak dependence on the concentrationof the candidate particle scattering colorant in the particle testmixture. Such dependence is usually so weak as to be unimportant for thedetermination of whether or not a material is a particle scatteringcolorant. However, for cases where a material is only marginally aparticle scattering colorant (or is marginally not a particle scatteringcolorant) the above described ratios of absorbances should be evaluatedat the concentration of the candidate particle scattering colorantintended for materials application. Also, it will be obvious to oneskilled in the art that the concentration of the candidate particlescattering colorant in the test mixture should be sufficiently high thatI/I_(o) deviates significantly from unity, but not so high that I is toosmall to reliably measure.

[0024] A particle scattering colorant candidate that does notsignificantly absorb in the visible has the A property if the particletest mixture has an effective maximum absorbance in the spectral regionof from about 380 to about 750 nm that is at least about 2 times andpreferably at least about 3 times the effective minimum absorbance inthe same wavelength range and the average particle size of the materialis below about 20 microns.

[0025] If the candidate particle scattering colorant is significantlyabsorbing in the visible, it can alternatively be determined to be aparticle scattering colorant if another material has the A property andthat material does not significantly absorb in the visible and hassubstantially the same distribution of particle sizes and shapes as thecandidate particle scattering colorant.

[0026] For scattering colorant candidates that significantly absorb inthe visible, the B property is also suitable for determining whether ornot a particulate material is a particle scattering colorant. Thedetermination of whether or not the B property criterion is satisfiedrequires the same measurement of effective absorbance spectra in thevisible region as used above. The B property criterion is satisfied ifthe candidate particle scattering colorant has a minimum in transmittedlight intensity that is shifted at least by 10 nm compared with thatobtained for the same composition having an average particle size above20 microns.

[0027] In another invention embodiment, a colorant is formed when smallparticles, called primary particles are embedded within large particles.For this case, one can determine whether or not the candidate materialis a particle scattering colorant by applying either the A propertycriterion or the B property criterion to either the primary particles orto the embedding particles that contain the primary particles.

[0028] These complexities in determining what is a particle scatteringcolorant disappear for invention embodiments of the second category,wherein the refractive index of a particle scattering colorant ismatched to that of the matrix material at some wavelength in thevisible. In such cases, any material that has a particle size less than2000 microns is a particle scattering colorant. Likewise, thedetermination of whether or not a candidate is a particle scatteringcolorant is readily apparent when it comprises a two-dimensional orthree-dimensional ordered array of primary particles. Large particles ofsuch particle scattering colorants will have an opal-like iridescencethat is apparent to the eye.

[0029] While the above determinations of whether or not a particulatematerial is a particle scattering colorant might seem complicated, theyare quite simple and convenient to apply. Particulate materials are mucheasier to disperse in liquids than they would be to disperse in thesolid matrices that provide the articles of this invention. Also, themeasurements of effective absorbance required for applying either the Aor B property criterion are rapid and can be accomplished byconventionally applied procedures using an inexpensive spectrometer.Hence, the application of these property criteria saves a great deal oftime in the identification of materials (i.e., particle scatteringcolorants) that are suitable for the practice of this invention.

[0030] In certain preferred embodiments of this invention, electronictransition colorants are used in conjunction with particle scatteringcolorants. An electronic transition colorant is defined as a materialthat has an absorption coefficient greater than 10⁻¹ cm⁻¹ at awavelength in the visible and does not satisfy the criteria for aparticle scattering colorant. Dyes and pigments are also used inconjunction with particle scattering colorants in embodiments of thisinvention. A dye or pigment is defined as a material that absorbs lightin the visible to a sufficient extent to confer visibly perceptiblecoloration. Depending on particle size, a pigment can either be aparticle scattering colorant or an electronic transition colorant. Also,in general, either electronic transition colorants, dyes, or pigmentscan be used interchangeably in invention embodiments.

[0031] In use, the particle scattering colorants used in the presentinvention are dispersed as particles in a surrounding matrix. Theseparticle scattering colorants particles can be either randomly locatedor arranged in a positionally correlated manner within a host matrix. Ineither case, intense coloration effects can occur as a consequence ofscattering from these particles. A positionally correlated arrangementof particle scattering colorants is preferred in order to achievecoloration effects that are somewhat flashy, and in some cases providedramatically different coloration for different viewing angles. Suchscattering processes for arrays of particles that have translationalorder are referred to as Bragg scattering. Non-correlated particlescattering colorants are preferred in order to achieve more subtlecoloration effects, which can be intense even for non-absorbing particlescattering colorants.

[0032] Since the visual limits of light radiation are approximatelybetween 380 and 750 nm, these limits are preferred to define the opticalcharacteristics of the particle scattering colorants for the purposes ofthe present invention. In some embodiments of the invention, theparticle scattering colorants that are preferred have a refractive indexthat is different from that of the host matrix throughout the entirevisible spectral range from 380 to 750 nm and particle scatteringeffects are preferably enhanced using electronic transition colorants,dyes or pigments. This situation differs from that of the Christiansenfilter materials of the prior art that provide matching of therefractive indices of host and matrix materials at least at onewavelength in the visible, and electronic transition colorants, dyes orpigments usually degrade performance. Unless otherwise specified, thedescribed refractive indices are those measured at room temperature.Also, a particle scattering colorant is said to have a differentrefractive index, a lower refractive index, or a higher refractive indexthan a matrix material if there exists a light polarization directionfor which this is true.

[0033] The particle scattering colorants, or a subcomponent thereof,should be small enough to effectively scatter light chromatically. Ifthere does not exist a visible wavelength at which a refractive index ofthe scattering particle colorant and the matrix are substantiallymatched, this means that the average particle size of such colorants ispreferably less than about 2 microns in the smallest dimension. Byaverage particle size we mean the ordinary arithmetic average, ratherthan (for example) the root-mean-square average. For embodiments of thisinvention where chromatic coloration occurs as a consequence of theexistence of a large difference between the refractive index of thematrix and the particle scattering colorant throughout the visiblespectral region, the average particle size for the particle scatteringcolorants is more preferably from about 0.01 to about 0.4 microns. Inthis case the average particle size in the smallest dimension is mostpreferably less than about 0.2 microns. Especially if the particlescattering colorant significantly absorbs light in the visible, evensmaller average particle sizes of less than 0.01 microns are within thepreferred range. Also, if the particle scattering colorant particles arenot preferentially oriented, it is preferable that the average ratio ofmaximum dimension to minimum dimension for individual particles of theparticle scattering colorant is less than about four and that theparticle scattering colorant particles have little dispersion in eitherparticle size or shape. On the other hand, for embodiments of thisinvention in which the refractive index of the particle scatteringcolorant and the matrix substantially vanishes at a visible wavelength,particle shapes can be quite irregular and preferred average particlesizes can be quite large, preferably less than about 2000 microns. Evenlarger particle sizes can be in the preferred range if the particlescattering colorant contains smaller particle scattering colorantswithin it. This complicated issue of preferred particle sizes fordifferent embodiments of the invention will be further clarified in thediscussion of these embodiments hereinafter.

[0034] Instead of expressing particle sizes by an average particle sizeor an average particle size in the smallest dimension, particle size fora particular particle scattering colorant can be expressed as thefraction of particles that have a smallest dimension that is smallerthan a described limit. Such description is most useful for theembodiments of this invention where the refractive index of the particlescattering colorant is much different than that of the matrix at allwavelengths in the visible. In such embodiments, it is preferable thatat least about 50% of all particles have a smallest dimension that isless than about 0.1 microns.

[0035] The matrix in which the particle scattering colorant is dispersedcan be either absorbing or non-absorbing in the visible spectral range.This absorption characteristic can be specified using eitherpath-length-dependent or path-length-independent quantities forcharacterization. For example, if an initial light intensity I_(o) isreduced to I_(t) by absorptive processes after the light passes througha matrix thickness t, then the percent transmission is 100(I_(t)/I_(o)).The corresponding absorption coefficient is −(1/t)ln((I_(t)/I_(o)).Unless otherwise specified, the described absorption characteristics arethose for a light polarization direction for which there is leastabsorption of light. For certain applications it is preferable for theparticle scattering colorant to be substantially non-absorbing in thevisible region. For other applications it is sufficient for the particlescattering colorant to not have a highest peak in absorption peak withinthe visible. In other applications that will be described, it ispreferable for the particle scattering colorant to have a maxima inabsorption coefficient at wavelengths that are within the visible. Thelatter provides invention embodiments in which the particle scatteringcolorant contains an overcoating layer of an absorbing material that issufficiently thin that it produces little light absorption.

[0036] Light scattering that is not strongly frequency dependent in thevisible region will often occur as a result of imperfections in a matrixmaterial. One example of such imperfections are crystallite-amorphousboundaries in semi-crystalline polymeric matrix materials. Suchnon-chromatic scattering can interfere with the achievement ofcoloration using particle scattering colorants. Consequently, it isuseful to define the “effective absorption coefficient” using the aboveexpressions, without correction for the scattering of the matrix thatdoes not arise from the particle scattering colorants.

[0037] Because of their utility for the construction of various articlesfor which novel optical effects are desired, such as carpets, clothing,wall paper, draperies, coverings for furniture, polymer molded parts,and coatings, organic polymers are preferred as matrix materials for thecompositions of this invention. By polymers we mean homopolymers,copolymers, and various mixtures thereof. Various inorganic and mixedorganic and inorganic matrix materials are also suitable for use asmatrix materials for the present invention, such as SiO₂ glasses, andmixtures of inorganic and organic polymers. The principal limitation onthe choice of such matrix materials is that either absorption orwavelength insensitive light scattering are not so dominant that thewavelength-selective scattering (i.e., chromatic scattering) due toparticle scattering colorants is negligible. This limitation means thatsuch matrix materials must have a degree of transparency. Using theabove defined effective absorption coefficient, this requirement oftransparency means that the effective absorption coefficient for thehost matrix in which the particle scattering colorant particles aredispersed is preferably less than about 10⁻⁴ Å Δn⁻¹ at some wavelengthin the visible spectra. More preferably, this effective absorptioncoefficient of the host matrix is less than about 10⁻⁵ Å⁻¹ at somewavelength in the visible, and most preferably this effective absorptioncoefficient is less than about 10⁻⁶ Å⁻¹ at some wavelength in thevisible. Numerous commercially available transparent organic polymershaving lower effective absorption coefficients in the visible areespecially suitable for use as matrix materials for the presentinvention. These include, for example, polyamides, polyurethanes,polyesters, polyacrylonitriles, and hydrocarbon polymers such aspolyethylene and polypropylene. Amorphous polymers having very littlescattering due to imperfections are especially preferred, such as anoptical quality polyvinyl, acrylic, polysulfone, polycarbonate,polyarylate, or polystyrene.

[0038] Depending on the intensity of coloration desired, the loadinglevel of the particle scattering colorant in the host matrix can bevaried over a very wide range. As long as the particle scatteringcolorants do not become aggregated to the extent that large refractiveindex fluctuations are eliminated at interfaces between particles, theintensity of coloration will generally increase with the loading levelof the particle scattering colorant. However, very high loading levelsof the particle scattering colorant can degrade mechanical propertiesand intimate particle aggregation can dramatically decrease interfacialrefractive index changes and alter the effective dimensions ofscattering particles. For this reason the volumetric loading level ofthe particle scattering colorant in the host matrix is preferably lessthat about 70%, more preferably less than about 30%, and most preferablyless than about 10%. However, in order to obtain a significantcoloration effect, the particle scattering colorant preferably comprisesat least about 0.01 weight percent of the matrix component, morepreferably at least about 0.1 weight percent of the matrix component,and most preferably at least about 1.0 weight percent of the matrixcomponent. Also, the required loading levels of particle scatteringcolorants can be lower for absorbing particle scattering colorants thanfor non-absorbing particle scattering colorants, and can be decreased incertain embodiments of the invention as either the refractive indexdifference between matrix and particle scattering colorant is increasedor the thickness of the matrix containing the particle scatteringcolorant is increased.

[0039] Various methods of particle construction can be employed in thematerials of the present invention for achieving the refractive indexvariations that are necessary in order to obtain strong particlescattering. Preferred methods include (1) the simple particle method,(2) the surface-enhanced particle method, and (3) the onion-skinparticle method. In the simple particle method, the particles aresubstantially uniform in composition and the refractive index of theseparticles is chosen to be different from that of the host matrix. Unlessotherwise noted, comments made herein regarding the refractive indexdifferences of particles and host matrices pertain either to theparticle refractive index for the simple particle method or the outerparticle layer for the case of more complex particles. In thesurface-enhanced particle method, the particles contain an overcoat ofan agent that has a refractive index which is different from that of thematrix. The refractive indices of the surface enhancement agent and thehost matrix should preferably differ by at least about 5%. Morepreferably, this refractive index difference is greater than about 25%.Finally, in the onion-skin particle method, the scattering particles aremulti-layered (like an onion skin) with layers having differentrefractive indices, so that scattering occurs from each interfacebetween layers. This refractive index difference is preferably greaterthan about 5%, although smaller refractive index differences can beusefully employed if a large number of layers are present in theonion-skin structure.

[0040] In one embodiment of this invention for the simple particlemethod the refractive index of the scattering particles is higher thanthat of the matrix. In another embodiment the refractive index of thematrix is higher than that of the scattering particles. In both theseembodiments the difference in refractive indices of the scatteringcenters and the matrix should be maximized in order to enhancecoloration due to particle scattering. Hence, these embodiments arereferred to as large Δn embodiments. More specifically, in the casewhere the scattering centers are inorganic particles and the matrix isan organic polymer, the difference in refractive index between theinorganic particles and the organic polymer should be maximized. Thisrefractive index difference will generally depend on the direction oflight polarization.

[0041] In other embodiments of this invention, the refractive index ofthe particle scattering colorants are closely matched at least at onewavelength in the visible. In these embodiments it is preferred that (1)there is a large difference in the wavelength dependence of therefractive index of the particle scattering colorant and the matrixpolymer in the visual spectral region, (2) the matrix polymer and theparticle scattering colorant have states that are optically isotropic,and (3) the neat matrix polymer has a very high transparency in thevisible. Such embodiments, called vanishing Δn embodiments, use theconcept of the Christiansen filter to obtain coloration. The size of theparticle scattering colorants are chosen so that all wavelengths in thevisible region are scattered, except those in the vicinity of thewavelength at which the refractive index of the matrix and the particlescattering colorant are matched. This wavelength dependence ofscattering efficiency either provides or enhances the articlecoloration.

[0042] Both the high Δn embodiments and the vanishing Δn embodimentsprovide the means for obtaining either stable coloration or switchablecoloration. In the high Δn embodiments, coloration that is switchable ina desired manner is preferably achieved using the combined effects ofparticle scattering and a wavelength-dependent absorption in the visiblethat is associated with an electronic transition. In the vanishing Δnembodiments, coloration that is switchable in a desired manner can beachieved by effects (light or actinic radiation exposure, thermalexposure, electric fields, temperature, humidity, etc.) that either (1)shift the wavelength at which Δn vanishes between two wavelengths withinthe visible range, (2) shift the wavelength at which Δn vanishes towithin the visible range, (3) shift the wavelength at which Δn vanishesto outside the visible range, or (4) causes a shift in coloration due tocombined effects of particle scattering and chromism in absorption inthe visible that is associated with an electronic transition colorant,dye or pigment. One of the discoveries of the present invention is thatferroelectric, switchable antiferroelectric compositions, andphotoferroelectric compositions provide preferred compositions forobtaining switchable coloration using particle scattering colorants.

[0043] Electronic transition colorants, dyes or pigments are especiallypreferred for obtaining switchable coloration for the high Δnembodiments, even when such colorants do not undergo a switching ofelectron absorption coloration. The reason can be seen by considering amaterial (such as a polymer film) that is sufficiently thin thatparticles do not scatter all of the incident visible radiation. In thiscase of the high Δn embodiment, the difference in refractive index ofthe particle scattering colorants and the matrix is large over theentire visible spectral range (compared with the wavelength dependenceof Δn over this range). Hence, changes in the refractive indexdifference between particle scattering colorant and matrix increases theoverall intensity of scattered light, which is generally approximatelyexponentially proportional to (Δn)², but does not substantially changethe wavelength distribution of such scattered light. On the other hand,the chromatic reflection and absorption of an electronic transitionabsorption colorant can provide switchability in the chromatic nature ofscattered light, since the amount of incident light effected by theelectronic transition colorant, dye or pigment can depend upon theamount of light that is not scattered by the particle scatteringcolorant. As an example, one may think of the situation where thescattering effectiveness and thickness of a particle scattering colorantlayer is so great that substantially no light is transmitted through toa layer containing an electronic transition colorant. If the refractiveindex of the particle scattering colorant is then switched so that therefractive index of the particle scattering colorant becomes much closerto that of the matrix, then light can be substantially transmittedthrough the particle scattering colorant layer to the electronictransition colorant layer. Then a switchability in the refractive indexof the particle scattering colorant provides a switchability in thecoloration of the article. This situation is quite different from thecase of the vanishing Δn embodiment, where, even in the absence of anelectronic absorption, an article that is sufficiently thin that it doesnot completely scatter light can evidence a switchability in thechromatic nature of scattered light. This can be true as long as thereis a switchability in the wavelength in the visible at which Δn vanishesand Δn significantly depends upon wavelength in the visible. Thewavelength dependence of refractive index in the visible is usefullyprovided as either n_(F)−n_(C) or the Abbe number((n_(D)−1)/(n_(F)−n_(C))), where the subscripts F, D, and C indicate thevalues of the refractive index at 486.1, 589.3, 656.3 nm, respectively.For the purpose of obtaining enhanced coloration for the vanishing Δnembodiment, the difference in nF−n_(C) for the particle scatteringcolorant and the matrix in which this colorant is dispersed ispreferably greater in absolute magnitude than about 0.001.

[0044] Particle scattering colorants and electronic transition colorantscan either be commingled together in the same matrix or mingled inseparate matrices that are assembled so as to be either substantiallymutually interpenetrating or substantially mutuallynon-interpenetrating. The latter case, where the particle scatteringcolorant and the electronic scattering colorant are in separate matricesthat are substantially mutually non-interpenetrating, provides the morepreferred embodiments of this invention, since the total intensity oflight scattered by the particle scattering colorant can thereby beoptimized. In this type of embodiment, the matrix containing theparticle scattering colorant is preferably substantially exterior tothat containing the electronic transition colorant on at least one sideof a fashioned article. So that the effects of both a electronictransition colorant and a non-absorbing particle scattering colorant canbe perceived, the thickness of the matrix containing the particlescattering colorant should be such that there exists a wavelength ofvisible light where from about 10% to about 90% light transmissionoccurs through the particle scattering colorant matrix layer, so as toreach the electronic transition colorant matrix layer. The preferredthickness of the electronic absorption colorant containing matrix layerthat underlies the particle scattering colorant containing layer (t_(e))depends upon the absorption coefficient of the electronic transitioncolorant at the wavelength in the visible at which the maximumabsorption occurs (λ_(m)), which is called α_(e), and the volumefraction of the matrix that is the electronic transition colorant(V_(e)). Preferably, α_(e)t_(e)V_(e) is greater than 0.1, whichcorresponds to a 9.5% absorption at λ_(m). Likewise, for the embodimentswhere the particle scattering colorant and the electronic absorptioncolorant are commingled in the same phase, it is useful to defineanalogous quantities for the particle scattering colorant (which aredenoted by the subscripts s), the only difference being α_(s) for theparticle scattering colorant includes the effects of both lightabsorption and light scattering on reducing the amount of lighttransmitted through the material and α_(s) depends on particle size. Forthese embodiments α_(e)V_(e) and α_(s)V_(s) preferably differ by lessthan a factor of about ten, and more preferably by a factor of less thanabout three. Likewise, preferred embodiments can be expressed for thecase of where the particle scattering colorant and the electronictransition colorant are located in separate phases (with volumes v_(s)and v_(e), respectively) that are substantially mutuallyinterpenetrating. In this case, α_(e)v_(e)V_(e) and α_(s)v_(s)V_(s)preferably differ by less than about a factor of ten, and morepreferably by a factor of less than about three.

[0045] The variation in refractive indices with composition for organicpolymers is relatively small compared with the corresponding variationfor inorganic particles. Typical average values for various unorientedorganic polymers at 589 nm are as follows: polyolefins (1.47-1.52),polystyrenes (1.59-1.61), polyfluoro-olefins (1.35-1.42), non-aromaticnon-halogenated polyvinyls (1.45-1.52), polyacrylates (1.47-1.48),polymethacrylates (1.46-1.57), polydienes (1.51-1.56), polyoxides(1.45-1.51), polyamides (1.47-1.58), and polycarbonates (1.57-1.65).Especially preferred polymers for use as polymer host matrices are thosethat have little light scattering in the visible due to imperfections,such as polymers that are either amorphous or have crystallite sizesthat are much smaller than the wavelength of visible light. The latterpolymers can be obtained, for example, by rapid melt-quenching methods.

[0046] Preferred scattering particles for combination in composites withpolymers having such low refractive indices in high Δn embodiments arehigh refractive index materials such as: 1) metal oxides such astitanium dioxide, zinc oxide, silica, zirconium oxide, antimony trioxideand alumina; 2) carbon phases such as diamond (n about 2.42),Lonsdaleite, and diamond-like carbon; 3) other high refractive indexinorganics such as bismuth oxychloride (BiOCl), barium titanate (n_(o)between 2.543 and 2.339 and n_(e) between 2.644 and 2.392 forwavelengths between 420 and 670 nm), potassium lithium niobate (n_(o)between 2.326 and 2.208 and n_(e) between 2.197 and 2.112 forwavelengths between 532 and 1064 nm), lithium niobate (n_(o) between2.304 and 2.124 and n_(e) between 2.414 and 2.202 for wavelengthsbetween 420 and 2000 nm), lithium tantalate (n_(o) between 2.242 and2.112 and n_(e) between 2.247 and 2.117 for wavelengths between 450 and1800 nm), proustite (n_(o) between 2.739 and 2.542 and n_(e) between3.019 and 2.765 for wavelengths between 633 and 1709 nm), zinc oxide(n_(o) between 2.106 and 1.923 and n_(e) between 2.123 and 1.937 forwavelengths between 450 and 1800 nm), alpha-zinc sulfide (n_(o) between2.705 and 2.285 and n_(e) between 2.709 and 2.288 for wavelengthsbetween 360 and 1400 nm), and beta-zinc sulfide (n_(o) between 2.471 and2.265 for wavelengths between 450 and 2000 nm). High refractive indexorganic phases are also preferred as particle scattering colorants foruse in low refractive index phases. An example of a high refractiveindex organic phase that can be used as a particle scattering colorantwith a low refractive index organic matrix phase (such as apolyfluoro-olefin) is a polycarbonate or a polystyrene. As isconventional, n_(o) and n_(e) in the above list of refractive indicesdenote the ordinary and extraordinary refractive indices, respectively,for crystals that are optically anisotropic. The n_(o) refractive indexis for light propagating down the principal axis, so there is no doublerefraction, and the n_(e) refractive index is for light having apolarization that is along the principal axis.

[0047] For the case where a high refractive index matrix is needed inconjunction with low index scattering particles, preferred particlescattering colorants are 1) low refractive index materials, such asfluorinated linear polymers, fluorinated carbon tubules, fluorinatedgraphite, and fluorinated fullerene phases, 2) low refractive indexparticles such as cavities filled with air or other gases, and 3) lowrefractive index inorganic materials such as either crystalline oramorphous MgF₂. Various inorganic glasses, such as silicate glasses, arepreferred for use as particle scattering colorants in many organicpolymer matrices for the vanishing Δn embodiments. The reason for thispreference is that such glasses are inexpensive and can be convenientlyformulated to match the refractive index of important, commerciallyavailable polymers at one wavelength in the visible. Also, thedispersion of refractive index for these glasses can be quite differentfrom that of the polymers, so that substantial coloration effects canappear in particle scattering. Inorganic glasses are also preferred foruse in high Δn embodiments, although it should be clear that the hostmatrix chosen for a high Δn embodiment for particular glass particlesmust have either a much higher or a much lower refractive index than thematrix chosen for a vanishing Δn embodiment for the same glassparticles. For example a glass having a refractive index of 1.592 wouldbe a suitable particle scattering colorant for polystyrene in thevanishing Δn embodiment, since polystyrene has about this refractiveindex. On the other hand, poly(heptafluorobutyl acrylate), withrefractive index of 1.367 could be used with the same glass particles ina high Δn embodiment. Relevant for constructing these colorant systems,note that the refractive indices of common glasses used in opticalinstruments range from about 1.46 to 1.96. For example, the refractiveindices of ordinary crown, borosilicate crown, barium flint, and lightbarium flint extend from 1.5171 to 1.5741 and the refractive indices ofthe heavy flint glasses extend up to about 1.9626. The values ofn_(F)−n_(C) for these glasses with refractive indices between 1.5171 and1.5741 range between 0.0082 and 0.0101. The corresponding range of theAbbe number is between 48.8 and 59.6. A refractive index that is on thelower end of the above range for commonly used optical glasses isobtained for fused quartz, and this material is also a preferredparticle scattering colorant. The refractive index for fused quartzranges from 1.4619 at 509 nm to 1.4564 at 656 nm.

[0048] Ferroelectric ceramics (such as the above mentioned bariumtitanate and solid solutions of BaTiO₃ with either SrTiO₃, PbTiO₃,BaSnO₃, CaTiO₃, or BaZrO₃) are preferred compositions for the particlescattering colorant phase of the compositions of the present invention.The reason for this preference is two-fold. First, very high refractiveindices are obtainable for many such compositions. For high Δnembodiments, these high refractive indices can dramatically enhancecoloration via an enhancement in scattering due to the large refractiveindex difference with respect to that of the matrix phase. Second, ifmatrix and host phases are matched in refractive index at a particularwavelength in the absence of an applied field (as for the vanishing Δnembodiments), an applied electric field can change the wavelength atwhich this match occurs—thereby providing a switching of color state.Alternatively, a ferroelectric phase that is an organic polymer can beselected to be the host phase. If a particle phase is again selected tomatch the refractive index of the unpoled ferroelectric at a particularwavelength, the poling process can introduce an electrically switchedchange in coloration. Such matching of the refractive index of hostphase and particle scattering colorant can be one that exists only for aspecified direction of light polarization. However, it is most preferredthat the matrix material and the particle scattering colorant havelittle optical anisotropy, so that the match of refractive indices islargely independent of light polarization direction.

[0049] Ceramics that are relaxor ferroelectrics are preferredferroelectrics for use as particle scattering colorant phases. Theserelaxor ferroelectrics have a highly diffuse transition betweenferroelectric and paraelectric states. This transition is characterizedby a temperature T_(m), which is the temperature of thefrequency-dependent peak in dielectric constant. As is conventional, weherein call T_(m) the Curie temperature (T_(c)) of a relaxorferroelectric, even though such ferroelectrics do not have a singletransition temperature from a purely ferroelectric state to a purelyparaelectric state. Relaxor ferroelectrics are preferred ferroelectricsfor use as particle scattering colorants when electric-field-inducedswitching in coloration is desired, since such compositions can displayvery large field-induced changes in refractive indices. Since thesefield-induced refractive index changes generally decrease as particlediameters become small, the particle dimensions should be selected to beas large as is consistent with achieving desired coloration states.

[0050] Relaxor ferroelectrics that are preferred for the presentinvention have the lead titanate type of structure (PbTiO₃) and disorderon either the Pb-type of sites (called A sites) or the Ti-type of sites(called B sites). Examples of such relaxor ferroelectrics having B sitecompositional disorder are Pb(Mg_(⅓)Nb_(⅔))O₃ (called PMN),Pb(Zn_(⅓)Nb_(⅔)) O₃ (called PZN), Pb(Ni_(⅓)Nb_(⅔))O₃ (called PNN), Pb(Sc_(½)Ta_(½)) O₃, Pb(Sc_(½)Nb_(½))O₃ (called PSN) , Pb(Fe_(½)Nb_(½))O₃(called PFN), and Pb(Fe_(½)Ta_(½))O₃. These are of the formA(BF_(⅓)BG_(⅔))O₃ and A(BF_(½)BG_(½))O₃, where BF and BG represent theatom types on the B sites. Further examples of relaxor ferroelectricswith B-site disorder are solid solutions of the above compositions, suchas (1−x)Pb(Mg_(⅓)Nb_(⅔))O₃—xPbTiO₃ and (1−x)Pb(Zn_(⅓)Nb_(⅔))O₃—xPbTiO₃.Another more complicated relaxor ferroelectric that is preferred for thepresent invention is Pb_(1−x) ²+La_(x) ³⁺ (Zr_(y)Ti_(z))_(1−x/4)O₃,which is called PLZT.

[0051] PZT (lead zirconate titanate, PbZr_(1−x)Ti_(x)O₃) is anespecially preferred ferroelectric ceramic for use as a particlescattering colorant. PMN (lead magnesium niobate, Pb(Mg_(⅓)Nb_(⅔))O₃) isanother especially preferred material, which becomes ferroelectric belowroom temperature. Ceramic compositions obtained by the addition of up to35 mole percent PbTiO₃ (PT) to PMN are also especially preferred for useas a particle scattering colorant, since the addition of PT to PMNprovides a method for varying properties (such as increasing the Curietransition temperature and varying the refractive indices) and since arelaxor ferroelectric state is obtainable using up to 35 mole percent ofadded (i.e., alloyed) PT.

[0052] Ceramic compositions that undergo a field-induced phasetransition from the antiferroelectric to the ferroelectric state arealso preferred for obtaining composites that undergoelectric-field-induced switching of coloration. One preferred family isthe Pb_(0.97)La_(0.02)(Zr, Ti, Sn)O₃ family that has been found byBrooks et al. (Journal of Applied Physics 75, pp. 1699-1704 (1994)) toundergo the antiferroelectric to ferroelectric transition at fields aslow as 0.027 MV/cm. Another family of such compositions is leadzirconate-based antiferroelectrics that have been described by Oh et al.in “Piezoelectricity in the Field-Induced Ferroelectric Phase of LeadZirconate-Based Antiferroelectrics”, J. American Ceramics Society 75,pp. 795-799 (1992) and by Furuta et al. in “Shape Memory Ceramics andTheir Applications to Latching Relays”, Sensors and Materials 3,4, pp.205-215 (1992) . Examples of known compositions of this type, referredto as the PNZST family, are of the general formPb_(0.99)Nb_(0.02)[(Zr_(0.6)Sn_(0.4))_(1−y)Ti_(y)]_(0.98)O₃.Compositions included within this family display field-inducedferroelectric behavior that is maintained even after the poling field isremoved. Such behavior is not observed for Type I material (y=0.060),where the ferroelectric state reconverts to the antiferroelectric statewhen the field is removed. However, type II material (y=0.63) maintainsthe ferroelectric state until a small reverse field is applied and thetype III material (y=0.065) does not revert to the antiferroelectricstate until thermally annealed at above 50° C. Reflecting these propertydifferences, the type I material can be used for articles that changecoloration when an electric field is applied, and revert to the initialcolor state when this field is removed. On the other hand, the type IIand type III materials can be used to provide materials in which theelectric-field-switched color state is stable until either a field inthe reverse direction is applied or the material is thermally annealed.

[0053] Ferroelectric polymer compositions are suitable for providingeither the particle scattering colorant or the matrix material for acomposite that is electrically switchable from one color state toanother. The term ferroelectric polymer as used herein includes bothhomopolymers and all categories of copolymers, such as random copolymersand various types of block copolymers. This term also includes variousphysical and chemical mixtures of polymers. Poly(vinylidene fluoride)copolymers, such as poly(vinylidene fluoride-trifluoroethylene),P(VDF-TrFE), are preferred ferroelectric polymer compositions.Additional copolymers of vinylidene fluoride that are useful for thecomposites of the present invention are described by Tournut inMacromolecular Symposium 82, pp. 99-109 (1994). Other preferredferroelectric polymer compositions are the copolymers of vinylidenecyanide and vinyl acetate (especially the equal mole ratio copolymer)and odd nylons, such as nylon 11, nylon 9, nylon 7, nylon 5, nylon 3 andcopolymers thereof.

[0054] Other particle scattering colorants include those that areabsorbing particle scattering colorants. One preferred family of suchabsorbing particle scattering colorants are colloidal particles ofmetals (such as gold, silver, platinum, palladium, lead, copper, tin,zinc, nickel, aluminum, iron, rhodium, osmium, iridium, and alloys,metal oxides such as copper oxide, and metal salts). Preferably theparticles are less than about 0.5 micron in average dimension. Morepreferably the particles are less than about 0.1 microns in averagedimension. In order to achieve special coloration effects, particles aremost preferred that are less than about 0.02 microns in averagedimension. Particles that have colloid-like dimensions are hereinreferred to as colloidal particles, whether or not colloid solutions canbe formed. Particle sizes that are below about 0.02 microns areespecially useful for obtaining a wide range of coloration effects fromone composition of absorbing particle scattering colorant, since thesesmall sizes can provide particle refractive indices and absorptioncoefficient maxima that depend upon particle size. This size variationof the wavelength dependent refractive index and absorption coefficientis most strongly enhanced for particles that are sometimes referred toas quantum dots. Such quantum dot particles preferably have a narrowparticle size distribution and an average particle size that is fromabout 0.002 to about 0.010 microns.

[0055] Convenient methods for forming colloidal particles include thevarious methods well known in the art, such as reaction of a metal saltin a solution or the crystallization of materials in confined spaces,such as solid matrices or vesicles. Likewise, well-known methods forproducing colloidal particles can be employed wherein colloid sizeliquid or solid particles dispersed in a gas or a vacuum are eitherreacted or otherwise transformed into solid particles of desiredcomposition, such as by crystallization. As an example of formation ofcolloidal particles that are useful for the present invention bysolution reaction methods, note that Q. Yitai et al. have described (inMaterials Research Bulletin 30, pp. 601-605 (1995)) the production of0.006 micron diameter zinc sulfide particles having a very narrowparticle distribution by the hydrothermal treatment of mixed sodiumsulfide and zinc acetate solutions. Also, D. Daichuan et al. havereported (in Materials Research Bulletin 30, pp. 537-541 (1995)) theproduction of uniform dimension colloidal particles of β-FeO(OH) by thehydrolysis of ferric salts in the presence of urea using microwaveheating. These particles had a rod-like shape and a narrow sizedistribution. Using a similar method (that is described in MaterialsResearch Bulletin 30, pp. 531-535 (1995)), these authors have madecolloidal particles of α-FeO having a uniform shape (and dimensions)that can be varied from a tetragonal shape to close to spherical (withan average particle diameter of about 0.075 microns).

[0056] Fiber-like particle scattering colorants having a colloid-likesize in at least two dimensions are also preferred for certain inventionembodiments, especially where anisotropic coloration effects aredesired. One unusual method for forming very small fibers that can beused as particle scattering colorants is by the deposition of a materialwithin the confining space of a hollow nano-scale fiber. The particlescattering colorant can then either comprise the filled nano-scalediameter fiber, or the fiber of the filler that is obtained by removing(by either physical or chemical means) the sheath provided by theoriginal hollow fiber. The general approach of making such fibers by thefilling of nano-size hollow fibers is taught, for example, by V. V.Poborchii et al. in Superlattices and Microstructures, Vol. 16, No. 2,pp. 133-135 (1994). These workers showed that about 6 nm diameternano-fibers can be obtained by the injection and subsequentcrystallization of molten gallium arsenide within the 2 to 10 nmchannels that are present in fibers of chrysotile asbestos. An advantageof such small dimension particles, whether in fiber form or not, is thatthe quantum mechanical effects provide refractive indices and electronictransition energies that strongly depend upon particle size. Hence,various different coloration effects can be achieved for a particlescattering colorant by varying particle size. Also, high dichroism inthe visible can be obtained for colloidal fibers of metals andsemiconductors, and such high dichroism can result in novel visualappearances for articles that incorporate such fibers as particlescattering colorants.

[0057] Colloidal particle scattering colorants, as well as particlescattering colorants that have larger dimensions, that comprise an outerlayer that absorbs in the visible are among preferred particlescattering colorants for use in high Δn embodiments. In such high Δnembodiments there is a large refractive index difference between theparticle scattering colorant and the matrix in the visible wavelengthrange. The reason for this preference is that a very thin layer of avisible-light-absorbing colorant on the outside of a colorless particlescattering colorant can dramatically enhance scattering at theparticle-matrix interface, while not substantially increasing lightabsorption. In order to achieve the benefits of such particle scatteringcolorant configuration, it is preferred that (1) the coating of thevisible-light-absorbing colorant on the surface of the particlescattering colorant comprises on average less than 50% of the totalvolume of the particles of the particle scattering colorant, (2) theaverage particle size of the particle scattering colorant is less that 2microns, and (3) the refractive index of the coating of the particlescattering colorant differs from that of the matrix in which theparticle scattering particle is dispersed by at least 10% at visiblewavelengths. More preferably, the coating of the visible-light-absorbingcolorant on the surface of the particle scattering colorant comprises onaverage less than about 20% of the total volume of the particles of theparticle scattering colorant and the average particle size of theparticle scattering colorant is less that 0.2 microns. Preferredapplications of such surface-enhanced particle scattering colorants arefor polymer fibers, polymer films, and polymer molded articles. A methodfor the fabrication of colloidal particles containing avisible-light-absorbing colorant on the surface of a colorless substrateparticle is described by L. M. Gan et al. in Materials Chemistry andPhysics 40, pp. 94-98 (1995). These authors synthesized barium sulfateparticles coated with a conducting polyaniline using an inversemicroemulsion technique. The sizes of the composite particles (fromabout 0.01 to 0.02 microns) are convenient for the practice of the highΔn embodiments of the present invention.

[0058] Colloid particles can either be added to the matrix in thecolloid-form or the colloid particles can be formed after addition tothe matrix. Likewise, these processes of colloid formation anddispersion can be accomplished for a precursor for the matrix, which issubsequently converted to the matrix composition by chemical processes,such as polymerization. For example, if the matrix is an organicpolymer, such as nylon, the metal colloids can be formed in a liquid,mixed with the ground polymer, and heated above the melting point of thepolymer to produce nylon colored with particle scattering colorants. Onthe other hand, either colloidal metal particles or a precursor thereofcan be added to the monomer of the polymer, the colloid particles can beformed in the monomer, and the monomer can then be polymerized. Aprecursor for a metal colloid can also be added to the polymer matrixand the colloidal particles can be then formed in a subsequent step.Such processes of colloidal particle formation and incorporation can befacilitated by using a melt, dissolved, gel, or solvent-swollen state ofthe polymer (or a precursor thereof) during colloid incorporation,colloid formation, or colloid formation and incorporation.Alternatively, high energy mechanical commingling involving a solidstate of the polymer (or a precursor thereof) can be used to accomplishcolloid incorporation, colloid formation, or colloid formation andincorporation.

[0059] The incorporation of colloidal size particle scattering colorantsin the gel state of a polymer prior to the formation of said gel stateinto a polymer fiber provides a preferred embodiment of this invention.For such process, the particle scattering colorant should preferablyhave a refractive index that is at least 10% different from that of thesolid polymer matrix of the fiber at a wavelength in the visible. Theaverage particle size of the particle scattering colorant is preferablyless than about 0.2 microns, more preferably less than about 0.08microns, and most preferably less than about 0.02 microns. For particlesizes of less than about 0.02 microns, the particle scattering colorantspreferably significantly absorbs in the visible. For the case where theparticle scattering colorant is substantially non-absorbing in thevisible, the polymer fiber preferably comprises an electronic transitioncolorant that is commingled with the particle scattering colorant in thegel state. Preferably this electronic transition colorant issubstantially a black carbon form, such as carbon black, and theparticle scattering colorant comprises an inorganic composition. So asnot to interfere with fiber strength, both the particle scatteringcolorant and optional electronic transition colorant particle used forthese fibers should have very small dimensions, preferably less thanabout 0.02 microns. Such invention embodiments solve a long standingproblem that arises for the coloration of high strength fibers that arespun in the gel state, such as high molecular weight polyethylene thatis spun from a mineral oil gel. This problem is that conventionalorganic dyes or pigments can interfere with the formation of highquality product from the gel state. An important example of a highstrength fiber product spun from the gel state is Spectra™ polyethylenefiber made by AlliedSignal. These fibers, which are gel processed athigh temperatures, are widely used for fishing lines, fishing nets,sails, ropes, and harnesses. The absence of satisfactory prior methodsfor achieving coloration has been a problem in the art.

[0060] Ultrafine metal particles suitable for use as particle scatteringcolorants can be located on the surface of much larger particles thatare themselves particle scattering colorants. Combined-particlescattering colorants of this form are also suitable for the presentinvention. Methods for the preparation of such particle scatteringcolorants, where metal particles are deposited on much larger polymerparticles, are provided by H. Tamai et. al. in the Journal of AppliedPhysics 56, pp. 441-449 (1995). As another alternative, colloidalparticle scattering colorants can be located within larger particlesthat, depending upon their dimensions and refractive index in thevisible (relative to the matrix) can additionally provide particlescattering coloration. In any case, the larger particles are referred toas particle scattering colorants as long as the included particles areparticle scattering colorants. In a preferred case, the colloidalparticles are metal or metal alloy particles in a glass matrix. Methodsfor obtaining colloidal copper dispersed in SiO₂-comprising glass aredescribed in the Journal of Non-crystalline Solids 120, pp. 199-206(1990) and methods for obtaining silicate glasses containing colloidalparticles of various metals, including gold and silver, are described inU.S. Pat. Nos. 2,515,936; 2,515,943, and 2,651,145, which areincorporated herein by reference. These glasses containing colloidalparticle scattering colorants are transformed to particles, such as bygrinding of melt processes, and used as particle scattering colorants inembodiments of this invention. In such embodiments, these particlescattering colorants are preferably dispersed in a polymer matrix,thereby providing particle scattering coloration for articles consistingof the resulting polymer composite.

[0061] An advantage of this colloid-within-particle design of theparticle scattering colorant is that the glass particles can stabilizethe colloidal particles with respect to degradation processes, such asoxidation. A second advantage is that high temperature methods can beused for forming the colloid in the glass, which could not be used forthe dispersion of the colloidal particles directly in an organic polymermatrix. A third advantage of the colloid-within-particle method is thatthe processes of colloid formation and dispersion are separated from theprocesses of dispersion of the particle scattering colorant in the finalpolymer matrix, which can provide improved process economics. As analternative to the melt synthesis of colloid-within-particle particlescattering colorants, such colorants can be synthesized by a method usedby K. J. Burham et al., which is described in Nanostructure Materials 5,pp. 155-169 (1995). These authors incorporated colloidal particles insilica by doping metal salts in the silanes used for the sol-gelsynthesis of the silicate. By such means they obtained Ag, Cu, Pt, Os,CO₃C, Fe₃P, Ni₂P, or Ge colloidal particles dispersed in the silica. Forthe purposes of the present invention embodiment, colloidal particlesdispersed in silica can be ground into suitable particle sizes for useas particle scattering colorants.

[0062] Instead of an inorganic glass, the particle containing thecolloid particles can be a polymer. It is known in the art to preparefilms of colloidal dispersions of various metals in the presence ofvinyl polymers with polar groups, such as poly(vinyl alcohol),polyvinylpyrrolidone, and poly(methyl vinyl ether). Particle scatteringcolorants suitable for the present invention embodiment can be obtainedby cutting or grinding (preferably at low temperatures) a polymer filmformed by solvent evaporation of the colloidal dispersion. Morepreferably, such particle scattering colorants can be formed byeliminating the solvent from an aerosol comprising colloidal particlesdispersed in a polymer-containing solvent. Particle scattering colorantsthat are either semiconductors or metallic conductors are amongpreferred compositions for use in polymer fibers. Such particlescattering colorants will generally provide significant absorption atvisible wavelengths. In such case it is preferred that the particlescattering colorant has an average diameter in the smallest dimension ofless than about 2 microns, the neat polymer matrix is substantiallynon-absorbing in the visible, and the minimum in transmitted visiblelight intensity for the particle scattering colorant is shifted by atleast by about 10 nm as a result of the finite particle size of theparticle scattering colorant. More preferably, this shift is at leastabout 20 nm for the chosen particle sizes of the particle scatteringcolorant and the chosen matrix material. For assessing the effect ofparticle size on the minimum of transmitted light intensity, a particlesize above about 20 microns provides a good approximation to theinfinite particle size limit.

[0063] For particle scattering colorant compositions that provide asingle maximum in absorption coefficient within the visible range whenparticle sizes are large, another application of the standardtransmitted light intensity ratio enables the identification ofpreferred particle scattering colorants. This method is to identifythose particle scattering colorants that have at least two minima intransmitted light intensity ratio that occur within the visiblewavelength range. Such two minima, possibly in addition to other minima,can result from either a bimodal distribution of particle sizes, ordifferences in the minimum resulting from absorptive processes andscattering processes for a mononodal distribution of particle sizes. Ifthe particle scattering colorants are required for applications in whichswitchability in coloration states are required, it is preferable thatthese two minima arise for a mononodal distribution in particle sizes.The reason for this preference is that the switchability in therefractive index difference between matrix and particle scatteringcolorant can provide switchable coloration if particle scatteringeffects are dominant. Mononodal and bimodal particle distributions,referred to above, designate weight-fraction particle distributions thathave one or two peaks, respectively.

[0064] For applications in which reversible color changes in response totemperature changes are desired, particular ceramics that undergoreversible electronic phase changes are preferred particle scatteringcolorants for the present invention. Such compositions that undergoreversible transitions to highly conducting states upon increasingtemperature are VO₂, V₂O₃, NiS, NbO₂, FeSi₂, Fe₃O₄, NbO₂, Ti₂O₃, Ti₄O₇,Ti₅O₉, and V_(1−x)M_(x)O₂, where M is a dopant that decreases thetransition temperature from that of VO₂ (such as W, Mo, Ta, or Nb) andwhere x is much smaller than unity. VO₂ is an especially preferredcolor-changing particle additive, since it undergoes dramatic changes inboth the real and imaginary components of refractive index at aparticularly convenient temperature (about 68° C.). The synthesis andelectronic properties of these inorganic phases are described by Specket al. in Thin Solid Films 165, 317-322 (1988) and by Jorgenson and Leein Solar Energy Materials 14, 205-214 (1986).

[0065] Because of stability and broad-band ability to absorb light,various forms of aromatic carbon are preferred electronic transitioncolorants for use in enhancing the coloration effects of particlescattering colorants. Such preferred compositions include various carbonblacks, such as channel blacks, furnace blacks, bone black, and lampblack. Depending upon the coloration effects desired from the combinedeffects of the particle scattering colorant and the electronic colorant,various other inorganic and organic colorants that are conventionallyused by the pigment and dye industry are also useful. Some examples ofsuch inorganic pigments are iron oxides, chromium oxides, leadchromates, ferric ammonium ferrocyanide, chrome green, ultramarine blue,and cadmium pigments. Some examples of suitable organic pigments are azopigments, phthalocyanine blue and green pigments, quinacridone pigments,dioxazine pigments, isoindolinone pigments, and vat pigments.

[0066] The use of either electronic transition colorants that aredichroic or a dichroic matrix composition can be used to provide novelappearances. Such novel appearances can result, for example, since thescattering of particle scattering colorants can display a degree ofpolarization. Preferential orientation of the dichroic axis ispreferred, preferably either parallel or perpendicular to the fiber axisfor a fiber or in the film plane for a film, and can be convenientlyachieved by conventionally employed methods used to make polarizers,such as mechanical drawing. The dichroic behavior can be usefullydeveloped either in the same matrix component in which the particlescattering colorant is dispersed or in a different matrix component. Onepreferred method for providing dichroic polymer matrix materials for thelarge Δn embodiments is by incorporating a dye molecule in the polymer,followed by uniaxially stretching the matrix containing the dyemolecule. Such a dye molecule serves as a dichroic electronic absorptioncolorant. The effect of the mechanical stretching process is topreferentially orientate the optical transition axis of the dye moleculewith respect to the stretch axis of the polymer. The creation ofpolarizing films by the mechanical stretching of a polymer host matrixis described by Y. Direx et al. in Macromolecules 28, pp. 486-491(1995). In the example provided by these authors, the dye was sudan redand the host matrix was polyethylene. However, various othercombinations of dye molecules and polymer matrices are suitable forachieving the polarizing effect that can be usefully employed in theparticle scattering colorant composites of the present inventionembodiments.

[0067] Various chemical compositions that are capable of providingswitchability in refractive index or adsorption coefficients are usefulfor either host matrices, particle scattering colorants, or electronictransition colorants that enhance the effects of scattering particlecolorants. In order to achieve novel coloration effects that areanisotropic, all of these switchable chemical compositions that areanisotropic can optionally be incorporated in a preferentiallyorientated manner in fabricated articles. By providing refractive indexand electronic transition changes that occur as a function of thermalexposure, light exposure, or humidity changes, such materials (eitherwith or without preferential orientation) provide a switchablecoloration state. A host of such color-changing chemicals suitable forthe present invention are well known, such as the anils, fulgides,spiropyrans, and other photochromic organics described in the book by A.V. El'tsov entitled “Organic Photochromes” (Consultants Bureau, NewYork, 1990). Such color changing chemicals can be employed as electronictransition colorants that modify the visual effect of particlescattering colorants in polymer composites. Also, color changes inresponse to temperature, light exposure, or humidity can alternativelybe produced by using the many well-known materials that providerefractive index changes in response to these influences, and nosignificant change in absorption coefficients at visible lightwavelengths. Such materials can be used as either the matrix material orthe particle scattering colorants for the color changing composites.

[0068] A host of photopolymerizable monomers, photo-dopable polymers,photo-degradable polymers, and photo cross-linkable polymers are alsoavailable for providing the switchable refractive indices and switchableelectronic absorption characteristics that enable the construction ofarticles having switchable particle scattering coloration. Materialssuitable for this use are described, for example, in Chapter 1 (pages1-32) written by J. E. Lai in the book entitled “Polymers for ElectronicApplications”, which is also edited by the same author (CRC Press, BocoRaton Fla., 1989). Improved materials that are now being introduced aredescribed by G. M. Wallraff et al. in CHEMTECH, pp. 22-30, April 1993.More exotic compositions suitable for the present application aredescribed by M. S. A. Abdou, G. A. Diaz-Guijada, M. I. Arroyo, and S.Holdcroft in Chem. Mater. 3, pp. 1003-1006 (1991).

[0069] Polymer colored articles of the present technology can alsocontain fillers, processing aids, antistats, antioxidants, antiozonants,stabilizers, lubricants, mold release agents, antifoggers, plasticizers,and other additives standard in the art. Unless such additivesadditionally serve desired purposes as particle scattering colorants orelectronic transition colorants, such additives should preferably eitherdissolve uniformly in the polymer that contains the particle scatteringcolorant or such additives should have a degree of transparency and arefractive index similar to the matrix polymer. Dispersing agents suchas surfactants are especially useful in the present invention fordispersing the particle scattering colorant particles. Many suitabledispersing agents and other polymer additives are well known in the artand are described in volumes such as “Additives for Plastics”, edition1, editors J. Thuen and N. Mehlberg (D.A.T.A., Inc., 1987). Couplingagents that improve the coupling between particle scattering particlesand host matrix are especially important additives for vanishing Δnembodiments, since they can eliminate fissure formation or poor wettingat particle-matrix interfaces. For cases where either a glass or aceramic is the particle scattering colorant, and the host matrix is anorganic polymer, preferred coupling agents are various silanes that arecommercially available and designed to improve bonding in compositesthat involve both inorganic and organic phases. Examples of suitablecoupling agents for particle scattering colorant composites of this typeare 7169-45B and X1-6124 from Dow Corning Company.

[0070] The colored articles of the present invention can optionallycontain materials that are either fluorescent or phosphorescent. Anexample of such known materials are of the form

[0071] Zn_(1−x)Cd_(x)S, where x is no greater than unity, that containsCu, Ag, or Mn impurities.

[0072] In various teachings of this invention we refer tophotopolymerizable monomers and oligomers. Examples of such compositionsthat are suitable for the practice of invention embodiments are monomerscontaining two of more conjugated diacetylene groups (that arepolymerizable in the solid state), vinyl ether terminated esters, vinylether terminated urethanes, vinyl ether terminated ethers, vinyl etherterminated functionalized siloxanes, various diolefins, various epoxies,various acrylates, and hybrid systems involving mixtures of the above.Various photoinitiators are also useful for such systems, such astriarylsulfonium salts.

[0073] Various methods can be employed for the compounding andfabrication of the composites of the present invention. For example,particle scattering colorants can be compounded with polymeric matrixmaterials via (1) melt-phase dispersion, (2) solution-phase dispersion,(3) dispersion in a colloidal polymer suspension, or (4) dispersion ineither a prepolymer or monomer for the polymer. Films of the compositecan be either formed by solvent evaporation or by adding a non-solventto a solution containing dispersed ceramic powder and dissolved polymerfollowed by sample filtration, drying, and hot pressing. In method (4),the ceramic particles can be dispersed in a monomer or prepolymer thatis later thermally polymerized or polymerized using actinic radiation,such as ultraviolet, electron-beam, or y-ray radiation. Particlescattering colorants can also be combined with the matrix byxerographic, power coating, plasma deposition, and like methods that arewell known in the art. For example, particle scattering colorants can beadded to fabrics or carpet by using xerography techniques described in“Printing Textile Fabrics with Xerography” (W. W. Carr, F. L. Cook, W.R. Lanigan, M. E. Sikorski, and W. C. Tinche, Textile Chemist andColorist, Vol. 23, no. 5, 1991). The coating of textile, carpet fiber,and wallpaper articles with particle scattering colorants in a fusiblepolymer matrix, so as to obtain coloration, is an especially importantembodiment because of the commercial importance of speedy delivery ofarticles that accommodate frequent style and color changes andindividual customer preferences. Such deposition can optionally bepreceded by a separate deposition of an electronic transition colorantin order to enhance the effect of the particle scattering colorant.

[0074] In order to obtain uniform mixing of the ceramic in the hostpolymer, ultrasonic mixers can be used in the case of low viscositycomposite precursor states and static mixers and more conventionalmixers can be used for melt blending processes. Static mixers, which areparticularly useful for melt blending processes, are availablecommercially from Kenics Corporation of Danvers, Mass., and aredescribed by Chen and MacDonald in Chemical Engineering, Mar. 19, 1973,pp. 105-110. Melt-phase compounding and melt-phase fabrication arepreferred for the compositions of the present invention. Examples ofuseful melt-phase fabrication methods are hot rolling, extrusion, flatpressing, and injection molding. For the fabrication of the morecomplicated shapes, injection molding and extrusion are especiallypreferred.

[0075] In some cases it is desirable to achieve a degree of controlledaggregation of the particle scattering colorants in order to achieveanisotropy in coloration effects. Such aggregation to produce anisotropyin coloration is preferably in either one dimension or two dimensions,wherein the direction of such aggregation for different particleaggregates are correlated. Such correlation in aggregation is mostconveniently achieved by plastic mechanical deformation of a matrix thatis heavily loaded with the particle scattering colorant. For example,such mechanical deformation can be in the fiber direction for a fiber orin either one or both of two orthogonal directions in the film plane fora film. As an alternative to using particle aggregation to achieveanisotropy in coloration, anisotropy in particle shape can be used toachieve the similar effects. For example, mechanical deformation offilms and fibers during processing will generally cause plate-likeparticles to preferentially orient with the plate plane orthogonal tothe film plane and fiber-like particles to preferentially orient withthe particle fiber axis parallel to the fiber axis of the composite.

[0076] A special type of particle scattering colorant orientation effectis specially useful for vanishing Δn embodiments. In such embodiments itis usually preferred that the particle scattering colorants and matrixmaterials are isotropic in optical properties. However, in order toobtain novel angle-dependent coloration effects, one can preferentiallyorient plate-like particles of an anisotropic particle scatteringcolorant in polymer films so that an optic axis of the particles isnormal to the film plane. Such particles and polymer matrix are chosenso that the ordinary refractive index (n_(o)) of the particles equalsthat of the matrix at a wavelength in the visible. Hence, a film articlewill appear highly colored when light perpendicular to the film plane istransmitted through the film. However, light that is similarly viewedthat is inclined to the film plane will be scattered at all wavelengthsso the article will appear either uncolored or less intensely colored.In such embodiments the particle scattering colorant is chosen to be onethat has the optic axis perpendicular to the particle plate plane, whichis the case for many materials having either hexagonal, trigonal, ortetragonal symmetry. Preferential orientation of the plane of theplate-like particles parallel to the film plane can be obtained byvarious conventional processes, such as film rolling processes, filmformation by solution deposition processes, and biaxial stretchingprocesses. Note that such plate-like particle scattering colorants arequite different from the plate interference colorants of the prior art.For these prior art colorants, no match of refractive indices of matrixand particle is require, and, in fact, large refractive indexdifferences between the particles and the matrix throughout the visiblecan increase the coloration effect.

[0077] Fibers of the present invention embodiments can either be formedby conventional spinning techniques or by melt fabrication of a filmfollowed by cutting the film into either continuous fibers or staple. Anelectronic transition colorant can be optionally included in thecomposite film composition. Alternately, a polymer film containing theparticle scattering colorant can be adhesively joined either to one sideor to both sides of a polymer film that contains an electronictransition colorant. The adhesive tie layer between these polymer filmlayers can be any of those typically used for film lamination. However,it is preferable to employ the same matrix polymer for the joined filmsand to select the tie layer to have about the same refractive index asthis matrix polymer. Alternately, the central film layer containingelectronic transition colorant and the outer film layers containing theparticle scattering colorant can be coextruded in a single step usingwell-known technologies of polymer film coextrusion. If the desired endproduct is a polymer fiber, these multilayer film assemblies can besubsequently cut into fiber form. Microslitter and winder equipment isavailable from Ito Seisakusho Co., Ltd (Japan) that is suitable forconverting such film materials to continuous fibers. Particularlyinteresting visual effects can be obtained if these fibers are cut froma bilayer film that consists of a polymer film layer containing theparticle scattering colorant on one side and a polymer film layercontaining an electronic transition colorant on the opposite side. Suchfibers that provide a different visual appearance for different viewingangles can be twisted in various applications, such as carpets andtextiles, to generate a spatially colored material due to the appearancein one viewing angle of alternating segments with different coloration.One coloration effect is provided if the fiber side that is in closestview is the particle scattering colorant film layer and anothercoloration effect is provided if the side that is in closest view is theelectronic transition colorant film layer. Such special colorationeffects of cut film fibers are most visually noticeable if the cut filmfiber strips have a width-to-thickness ratio of at least 5.Additionally, dimensional compatibility of such fiber for comminglingwith conventional polymer fibers in textile and carpet applications isincreased if the cut film fibers have a denier that is less than 200. Asan alternative to the slit-film process, either bilayer or multilayerfibers having these characteristics can be directly melt spun using aspinneret that is designed using available technology of spinnerets.This paragraph has emphasized the formation of fibers by the cutting ofpolymer films of this invention that provide particle scatteringcoloration effect. However, is should be emphasized that the films thathave been described also provide important commercial opportunities asfilm products for application in diverse areas, from product packagingon one extreme to wallpaper on another.

[0078] Sheath-core fibers which are suitable for the invention arefibers comprising a sheath of a first composition and a core of a secondcomposition. Either the sheath or the core can be organic, inorganic, ormixed inorganic and organic, independent of the composition of the othercomponent. Preferably both the sheath and core of such fibers containorganic polymer compositions. Also, the particle scattering colorant ispreferably located in the sheath and an electronic transition colorantis preferably located in the core. By choice of either sheath or corecross-sectional geometry that does not have circular cylindricalsymmetry, it is possible to provide fibers that provide differentcolorations when viewed in different lateral directions. For example,the external sheath geometry can be a circular cylinder and the core canbe an ellipse having a high aspect ratio. When viewed orthogonal to thefiber direction along the long axial direction of the ellipse, theeffect of the electronic transition colorant can dominate coloration. Onthe other hand, a corresponding view along the short axis of the ellipsecan provide a visual effect that is less influenced by the electronictransition colorant. More generally, in order to achieve such angledependent visual effects the maximum ratio of orthogonal axialdimensions in cross-section for the outer surface of the sheath ispreferably less than one-half of the corresponding ratio for the core.Alternatively, the sheath and core should preferably both have a maximumratio of orthogonal axial dimensions in cross-section that exceeds twoand the long-axis directions in cross-section of sheath and core shouldpreferably be unaligned. Such fibers that provide a different visualappearance for different viewing angles can be twisted in variousapplications, such as carpets and textiles, to generate a spatiallycolored material whose appearance in one viewing angle is determined byalternating segments with different coloration.

[0079] The ability to change the coloration of sheath-core fibers byvarying the relative cross-sections of sheath and core provides for theconvenient fabrication of yarns that display interesting visual effectsbecause of variations in the coloration of different fibers in the yarn.Such variation can be accomplished, for example, by varying the relativeor absolute sizes of the sheath and cores, their relative shapes, andthe relative orientation of the sheath and core cross-sections. For anyof these cases, the said variation can be provided either along thelength of individual fibers or for different fibers in a yarn.Preferably in these embodiments, the particle scattering colorant is inthe fiber sheath and an electronic transition colorant is in the fibercore. Also, a yarn consisting of such fibers is preferably assembleddirectly after spinning from a multi-hole spinneret. Variation in theindividual spinneret hole constructions, or variation in the feedpressures for the sheaths and cores for different fiber spinning holes,can permit the desired fiber-to-fiber variations in either sheathcross-section, the core cross-section, or both. Alternatively, variationin the coloration of individual fibers along their length can beachieved by convenient means. These means can, for example, be byvarying as a function of spinning time either (1) either the sheathpolymer feed pressure or the core polymer feed pressure or (2) therelative temperatures of the sheath and the core polymers at thespinneret. Of these methods, variation in coloration along the lengthsof individual fibers is preferred, and such variations are preferablyachieved by changing the relative feed pressures of the sheath and corefiber components. Such pressure variations are preferably accomplishedsimultaneously for the spinneret holes that are used to producedifferent fibers and such spinneret holes for different fibers arepreferably substantially identical. Yarns are preferably formed from thefibers at close to the point of spinning, so that correlation in thelocation of like colors for different fibers is not lost. As a result ofsuch preferred embodiment, the color variations of individual fibers arespatially correlated between fibers, so these color variations are mostapparent in the yarn.

[0080] The fact that fiber coloration depends upon both the sheath/coreratio and mechanical draw processes when the particle scatteringcolorant is in the sheath and the electronic transition colorant is inthe core provides important sensor applications. These sensorapplications utilize the coloration changes resulting from fiber wearand other fiber damage processes, such as the crushing of fibers whichcan provide coloration by deforming the cross-sections of sheath andcore, abrasion or fiber dissolution which can change the cross-sectionof the fiber sheath, and fiber stretching (which can change thecross-sections of sheath and core, provide particle scattering colorantaggregation, and increase both polymer chain orientation and fibercrystallinity). In any case, the basis for these color changes isgenerally a changing relative contribution from particle scatteringcolorant and electronic transition colorant to article coloration. Suchsensors can provide valuable indication of damage in articles such asropes, slings, and tire cord where the possibility of catastrophicfailure and uncertainties in when such failure might occur lead tofrequent article replacement. The sheath/core fibers of the presentinvention can be used either as a color-indicating minority or majorityfiber in such articles.

[0081] Special methods of this invention can be used to obtainparticle-induced coloration for fibers that are spun in hollow form. Theparticles that provide coloration via scattering can be dispersed in asuitable liquid, which subsequently fills the hollow fibers. Optionalelectronic transition colorants can be included in this liquid in orderto enhance the coloration effect. This approach is enabled by usingeither a precursor fiber that is staple (i.e., short open-ended cutlengths) or to use hollow fibers that contain occasional micro holes,where the hollow fiber core breaks to the surface. The existence ofthese micro holes enables rapid filling of the fibers. Modest pressuresof preferably less than 2000 psi can be used to facilitate rapid fillingof the fibers. A low viscosity carrier fluid is preferably chosen as onethat can be either photopolymerized or thermally polymerized after thefilling process. As an alternative to this approach, the particlescattering colorant can be included in molten polymer from which thehollow fibers are melt spun. Then the polymerizable fluid that is drawninto the hollow fiber after spinning can include an electronictransition colorant for enhancing the coloration effect of the particlescattering colorant. Various modifications of these methods can beemployed. For example, melt spun fibers can contain various combinationsof particle scattering and electronic transition colorants, as can thefluid that is drawn into the hollow fibers. As another variation ofthese methods, hollow fibers spun from a melt that contain a particlescattering colorant can be coated on the interior walls with a materialthat absorbs part of the light that is not scattered by the particlescattering colorant. For example, such coating can be accomplished bydrawing an oxidant-containing monomer solution for a conducting polymer,solution polymerizing the conducting polymer onto the interior walls ofthe hollow fibers, and then withdrawing the solution used forpolymerization from the hollow fibers. The inner walls of hollow fibersare preferably colored with an electronic transition colorant using asolution dye process that requires thermal setting. For example, a dyesolution can be imbibed into the hollow fibers by applying suitablepressure, any dye solution on the exterior surface of the fibers can bewashed away, the dye coloration can be set by thermal treatment, and thedye solution contained within the fibers can be removed (such as byevaporation of an aqueous solution). As an alternative to thermalsetting, the setting of the dye on the inner surface of the hollowfibers can be by either photochemical or heating effects of radiation,such as electron beam, ultraviolet, or infrared radiation. Such thermalor photoassisted setting of the dye can be accomplished in a patternedmanner, thereby providing fibers that display the type of spatialcoloration effects that are sought after for carpet and textileapplications.

[0082] The same methods above described for obtaining internal walldyeing of hollow fibers can be used for the achievement of novel opticaleffects via deposition of particle scattering colorants on the inside ofhollow fibers. These particle colorants are preferably deposited byimbibing a colloidal solution containing the particle scatteringcolorant into the hollow fibers and then evaporating the fluid that isthe carrier for the colloidal particles. The liquid in which thecolloidal particles are dispersed can optionally contain a material thatforms a solid matrix for the colloidal particles after fluid componentsare eliminated. Such colloidal particle scattering colorants, whetherdeposited on the inner walls as a neat layer or as a dispersion in amatrix, can then be optionally coated with an electronic transitioncolorant by methods described above for coating the inner walls ofhollow fibers that are not coated with particle scattering colorants.Note that the above described deposition of colloidal particles on theinside of hollow fibers can result in aggregation of these particles tothe extent that they transform from particle scattering colorants toelectronic transition colorants. Depending upon the coloration effectdesired, this aggregation can be either desirable or undesirable.

[0083] In the following embodiment of this invention, particlescattering colorants are used in hollow fibers to produce photochromism.Such photochromism can be achieved using particle scattering colorantsthat are photoferroelectrics. Preferred photoferroelectrics for thisapplication are, for example, BaTiO₃, SbNbO₄, KNbO₃, LiNbO₃, and suchcompositions with optional dopants such as iron. These and relatedcompositions are described in Chapter 6 (pp. 85-114) of“Photoferroelectrics” by V. M. Fridkin (Springer-Verlag, Berlin, 1979).Photovoltages of the order 103 to 105 volts can be- generated forphotoferroelectrics, although it should be recognized that thesephotovoltages decrease as the particle size in the polarizationdirection decreases. The corresponding photo-generated electric fieldscan be used to reversibly produce aggregation (i.e., particle chaining)of photoferroelectric particles that are dispersed in a low conductivityliquid within the cavity of a hollow fiber. If these photoferroelectricparticles have suitably small dimensions, aggregation and deaggregationprocesses will provide a photo-induced change in the visual appearanceand coloration of the fiber. The electrical conductivity of the fluidcan determine the rate of return of the coloration to the initial stateafter light exposure ceases, since this conductivity can lead to thecompensation of the photo-induced charge separation that provides thephoto-induced field. Methods described above can be used for the fillingof the hollow fibers with the photoferroelectric-containing liquid, andsuch liquid can be sealed in the fibers by a variety of processes, suchas by periodic closure of the hollow tubes using mechanical deformation.Articles consisting of these photochromic fibers can be used for variousapplications, such as clothing that automatically changes color uponlight exposure.

[0084] In another invention embodiment, the particle scattering colorantis a photoferroelectric that is dispersed in a solid matrix that has thesame refractive index as the photoferroelectric at some wavelength inthe visible (either when the photoferroelectric is not exposed to lightor after it has been exposed to light, or both). This embodiment usesthe large refractive index changes that occur upon the exposure of aphotoferroelectric to light, which shifts the wavelength at whichrefractive index matching occurs (or either causes or eliminates suchrefractive index matching), thereby causing a coloration change inresponse to light.

[0085] In previously discussed embodiments of this invention (forsheath-core fibers, trilayer and bilayers films and derived cut-filmfibers, and hollow polymer fibers), the use of particle scatteringcolorants in a layer that is exterior to the layer containing anelectronic transition colorant has been described. One described benefitis the novel coloration effects achieved. Another benefit of suchconfigurations is particularly noteworthy. Specifically, particlescattering colorants that provide blue coloration also generally providesignificant scattering in the ultraviolet region of the spectra that cancause the fading of many electronic transition colorants. Hence, thisultraviolet scattering can protect the underlying electronic transitioncolorants from fading due to ultraviolet light exposure.

[0086] Preferred embodiments result from the advantages of using aparticle scattering colorant to provide ultraviolet light protection forultraviolet-light sensitive fiber and film products. For articles inwhich the particle scattering colorant is dispersed in a first matrixmaterial that is substantially exterior to a second matrix componentcomprising an electronic transition colorant (such as for abovedescribed hollow fibers, sheath-core fibers, and trilayer films andderived cut-film fibers) it is preferred that (1) the first matrixcomponent and materials contained therein absorb less than about 90% ofthe total visible light that can be incident on the article from atleast one possible viewing angle, (2) the absorption coefficient of thefirst matrix component and materials contained therein is less thanabout 50% of that of the second matrix component and materials containedtherein at a wavelength in the visible, (3) and the particle scatteringcolorant is substantially non-absorbing in the visible. In addition, itis preferable that the first matrix component and materials containedtherein either absorb or scatter more than about 50% of uniformradiation at the ultraviolet wavelength at which the second matrixcomponent comprising the electronic dopant undergoes the maximum rate ofcolor fading. The term uniform radiation means radiation that has thesame intensity for all spherical angles about the sample. Uniformradiation conditions exist if there is the same radiation intensity forall possible viewing angles of the article. The average particle sizethat is most effective for decreasing the transmission of light througha matrix at a wavelength λ_(o) is generally greater than about λ_(o)/10and less than about λ_(o)/2. Hence, for maximum protection of anelectronic transition colorant that most rapidly fades at λ_(o), theaverage particle for the particle scattering colorant should preferablybe from about Δn _(o)/2 to about λ_(o)./10. Additionally, for thispurpose the particle scattering colorant should preferably beapproximately spherical (having an average ratio of maximum dimension tominimum dimension for individual particles of less than four) and thereshould be little dispersion in the sizes of different particles. Mostpreferably the average particle size for the particle scatteringcolorants used for ultraviolet light protection of electronic transitionpigments should be from about 0.03 to about 0.1 microns. Particlescattering colorants that are especially preferred for conferringultraviolet light protection for electronic transition colorants aretitanium dioxide and zinc oxide.

[0087] Materials suitable for the present art include inorganic ororganic materials that have any combination of organic, inorganic, ormixed organic and inorganic coatings. The only fundamental limitation onsuch a coating material is that it provides a degree of transparency inthe visible spectral region if the entire surface of the article iscovered with such a coating material. Preferred coating materials forapplication to film, fiber, or molded part surfaces are well-knownmaterials that are called antireflection coating materials, since theyminimize the reflectivity at exterior surfaces. Such antireflectioncoatings can enhance the visual effect of particle scatting colorants bydecreasing the amount of polychromatically reflected light.Antireflection coatings can be provided by applying a coating to thesurface of an article so that the refractive index of the coating isclose to the square root of the refractive index of the surface of thearticle and the thickness of the coating is close to λ/4, where λ is theapproximate wavelength of light that is most problematic. For example,antireflection coatings can be obtained by well known means for polymerssuch as polycarbonate, polystyrene, and poly(methyl methacrylate) byfluorination of the surface, plasma deposition of fluorocarbon polymerson the surface, coating of the surface with a fluoropolymer fromsolution, or in situ polymerization of a fluoromonomer that has beenimpregnated on the surface. Even when the refractive index of theantireflection polymer layer does not closely equal the square root ofthe refractive index of the surface of the article, light is incident atan oblique angle to the surface, and the wavelength of the lightsubstantially deviates from λ, antireflection properties suitable forthe present application can be obtained using such single layers.Furthermore, the known technologies of broadband, multilayerantireflection coatings can be used to provide antireflection coatingshaving improved performance. Hence, antireflection coatings can beprovided for essentially any substrate, such as a polymer film, thatdecrease the polychromatic surface reflection that can interfere withthe visual effect of particle scattering colorants.

[0088] The ability to arrange the light scattering particles in apatterned manner is important for achieving the spatial coloration thatis desirable for many articles, such as polymer fibers. A number ofprocesses can be used to achieve such spatial coloration. One method isto use the effect of magnetic fields on ordering magnetic colloidalfluids, such fluids being transformable into solid materials by thermalor photochemical setting. Such thermal setting is preferably either bydecreasing temperature to below a glass transition or meltingtemperature or by thermal polymerization. Such photochemical setting ispreferably by photo-polymerization to a glassy state. Another usefulsetting process is solvent evaporation from the colloidal suspension.Such setting should be substantially accomplished while the magneticmaterial is in a magnetic-field-ordered state, so that novel opticalproperties are conferred on the article by scattering and absorptiveeffects of the ordered magnetic material. Examples of magnetic colloidalsuspensions that can be used to provide novel coloration effects areeither water-based or organic-based suspensions of nanoscale magneticoxides. Such suspensions, called ferrofluids, are obtainablecommercially from Ferrofluidics Corporation, Nashua N.H. and aredescribed by K. Raj and R. Moskowitz in the Journal of Magnetism andMagnetic Materials, Vol. 85, pp. 233-245 (1990). One example of howmagnetic particles can be deposited in a spatially variant way isindicated by returning to the above examples of hollow fibers. Suchhollow fibers can be filled with a dispersion of the magnetic particlesin a polymerizable fluid. The magnetic particles can be spatiallydistributed in a desired pattern along the length of the hollow fibersusing a magnetic field. Finally, the fluid can be polymerized orcross-linked thermally or by exposure to actinic radiation in order toset the structure. Polyurethane thermosets provide one preferred type ofthermally set fluid for this application.

[0089] Spatially variant coloration of fibers and films can beaccomplished quite simply by mechanical drawing processes that varyalong the length of the fiber or film. Variation in the degree of drawcan provide variation in the refractive index of the polymer matrix andthe degree of stretch-induced crystallinity. These variations providespatially dependent variation in the coloration resulting from particlescattering colorants. For such spatially dependent variation ofcoloration to be visually perceived, predominant color changes shouldoccur less frequently than every 200 microns, unless the separationbetween regions having different optical properties is sufficientlyshort to provide diffraction grating or holographic-like effects.

[0090] Especially interesting and attractive visual effects can beachieved by the deposition of particle scattering colorants as a patternthat is spatially variant on the scale of the wavelength of light. Theresult of such pattering is the creation of a holographic-like effect.The preferred particle scattering colorants of the present inventionembodiment have refractive indices for all wavelengths in the visiblespectra which do not equal those of the host matrix at the samewavelength, which is in contrast with the case of Christiansen filters.In fact, it is preferable that the particle scattering colorants thatare patterned to provide the holographic effect differ from that of thematrix by at least about 10% throughout the visible region. Mostpreferably, this difference in refractive index of particle scatteringcolorant and host matrix is at least about 20% throughout the visibleregion of the spectra.

[0091] The effect of the particle scattering colorants on the colorationof polymer articles and the polymers contained therein can bedramatically decreased or even eliminated, which is an importantadvantage of the present technology—since it enables the recycling oforiginally colored polymers to provide polymer resin that has little orno coloration. Special embodiments of the present invention enable suchrecycling. In the first embodiment both particle scattering colorantsand electronic transition colorants are employed in different matrixpolymers, so that the coloration effect of the particle scatteringcolorant is substantial only in the presence of the electronictransition colorant (which absorbs non-scattered light so that thislight does not interfere with the visual effect of light that ischromatically scattered by the particle scattering colorant). In thisembodiment, the scattering colorant has no significant absorption in thevisible (or at least no significant absorption peak in the visible) andthe matrix polymer for the particle scattering colorant and electronictransition colorant are sufficiently different that separation byphysical or chemical means is viable. For example, this separation canbe accomplished by either dissolving only one of the matrix polymers orcausing the matrix polymer for the electronic transition colorant todepolymerize. The second embodiment employs colored articles thatpreferably contain only a particle scattering colorant. In this type ofrecycling method the coloration of the polymer is either decreased oreliminated by either (1) a thermal heating or irradiation process thateither decreases the refractive index difference between particlescattering colorant and the host matrix to a value that is small, buteither non-zero anywhere in the visible range or substantially zerothroughout all the visible range; (2) a thermal heating or irradiationprocess that either eliminates a match of refractive index betweenmatrix and particle scattering colorant at a wavelength in the visibleor causes such match to occur over a broad spectral range; or (3) eithera dissolution, evaporation, or chemical process that removes theparticle scattering colorant from the host matrix. For example, theparticle scattering colorant can be an organic composition thatevidences a high refractive index with respect to the matrix because ofthe presence of double bonds. Chemical processes (such asultraviolet-induced, four-centered coupling of double bonds to formcyclobutane rings) can dramatically decrease the refractive indexdifference of the particles and the matrix, thereby effectivelyeliminating the coloration. As another example, the particle scatteringcolorant can be chosen as one that is sublimable at temperatures atwhich the matrix polymer is thermally stable, one that is soluble insolvents that are non-solvents for the matrix polymer, or one thatdissolves in the matrix polymer. In all of these cases, the colorationof the polymer is either decreased or eliminated by either destroyingthe particles, decreasing the refractive index difference between theparticles and the matrix, eliminating a perfect match of refractiveindices of the particles and the matrix at only one wavelength, orseparating the particles from the matrix polymer. In fact, methods abovedescribed for obtaining switchable coloration of polymers (viarefractive index changes), which are useful for obtaining spatialcoloration effects in polymer articles, are also useful for eitherdecreasing or eliminating coloration during recycling processes. A thirdembodiment of this invention for providing recyclable colored polymersuses mechanical processes, such as polymer grinding, that cause eitheraggregation or stress-induced chemical reaction of the particlescattering colorant, thereby eliminating the effectiveness of theparticle scattering colorants for providing coloration.

[0092] The particle scattering colorant embodiments of the presentinvention that are described above do not necessarily require thearrangement of the individual particles as an array having translationalperiodicity. Such arrangement is sometimes desirable, since novel visualappearances can result, especially intense iridescent coloration. Theproblem is that it has been so far impossible to achieve such periodicarrangements in either the desired two or three dimensions on a timescale that is consistent with polymer processing requirements, which aredictated by economics. The presently described invention embodimentprovides an economically attractive method to achieve these novel visualeffects for polymers. The particle scattering colorants of thisembodiment consist of primary particles that are arranged in atranslationally periodic fashion in m dimensions, where m is either 2 or3. At least one translational periodicity of the particle scatteringcolorants is preferably similar to the wavelength of light in thevisible spectrum. More specifically, this preferred translationalperiodicity is from about 50 to about 2000 nm. More preferably thistranslational periodicity is from about 100 to about 1000 nm. In orderto obtain such translational periodicity, it is desirable for theparticle scattering colorant to consist of primary particles that havesubstantially uniform sizes in at least m dimensions. The particlescattering colorant can optionally comprise other primary particles,with the constraint that these other primary particles are either smallcompared with the above said primary particles or such other primaryparticles also have relatively uniform sizes in at least the said mdimensions. The average size of the primary particles in their smallestdimension is preferably less than about 500 nm.

[0093] The first step in the process is the preparation oftranslationally ordered aggregates of the primary particles. Since thisfirst step does not necessarily occur on the manufacturing lines forpolymer articles, such as fibers, films, or molded parts, theproductivity of such manufacturing lines need not be reduced by the timerequired for the formation of particle scattering colorants consistingof translationally periodic primary particles. The second step in theprocess is to commingle the particle scattering colorant with either thepolymer host matrix or a precursor thereof. Then, as a third step orsteps, any needed polymerization or crosslinking reactions can beaccomplished and articles can be fashioned from the matrix polymercontaining the particle scattering colorant particles. In order tooptimize desired visual effects, it is critically important that suchsecond and third step processes do not completely disrupt thetranslationally periodic arrangement of primary particles within theparticle scattering colorants. This can be insured in a number of ways.First, the average size of the particle scattering colorant particles inthe smallest dimension should preferably be less than about one-third ofthe smallest dimension of the polymer article. Otherwise mechanicalstresses during article manufacture can disrupt the periodicity of theprimary particles in the particle scattering colorant. The particlescattering colorant dimension referred to here is that for the particlescattering colorant in the shaped polymer matrix of the polymer article.However, it is also preferable that the particle sizes of the particlescattering colorant in the fashioned polymer matrix of the polymerarticle are those initially formed during the aggregation of the arraysof primary particles. The point is again that mechanical steps, such asmechanical grinding, should be avoided to the extent possible if thesesteps potentially disrupt the translation periodicity within theparticle scattering colorant, such as by the production of cracks orgrain boundaries within the particle scattering colorant.

[0094] Various methods can be used for the first step of forming theparticle scattering colorant particles containing translationallyperiodic primary particles. One useful method is described by A. P.Philipse in Journal of Materials Science Letters 8, pp. 1371-1373(1989). This article describes the preparation of particles having anopal-like appearance (having intense red and green scattering colors) bythe aggregation of silicon spheres having a substantially uniformdimension of about 135 nm. This article also teaches that the mechanicalrobustness of such particle scattering colorant having a threedimensionally periodic arrangement of silica spheres can be increased byhigh temperature (a few hours at 600° C.) treatment of the silica sphereassembly. Such treatment decreased the optical effectiveness of theparticle scattering colorant, since the particles became opaque.However, Philipse taught that the particle aggregates recover theiroriginal iridescent appearance when immersed in silicon oil for a fewdays. Such treatment (preferably accelerated using either appliedpressure, increased temperature, or a reduced viscosity fluid) can alsobe used to produce the particle scattering colorant used for the presentinvention. However, it is more preferable if the mechanical robustnessis achieved by either (1) forming the translationally periodic assemblyof spherical primary particles from a fluid that can be latterpolymerized, (2) either imbibing or evaporating a fluid to inside theas-formed translationally periodic particle assembly and thenpolymerizing this fluid, or (3) annealing the translationally periodicparticle assembly (as done by Philipse), either imbibing or evaporatinga fluid in inside this particle assembly, and then polymerizing thisfluid. Alternatively, materials can be dispersed inside the periodicarray of primary particles by gas phase physical or chemical deposition,such as polymerization from a gas phase. Such methods and relatedmethods that will be obvious to those skilled in the art can be employedto make the particle scattering colorants that are used in the presentinvention embodiment. For example, the primary particles can be eitherorganic, inorganic, or mixed organic and inorganic. Likewise, theoptional material that is dispersed within the array of primaryparticles in the particle scattering colorants can be organic,inorganic, or mixed organic and inorganic. In cases where the particlescattering dolorants would be too opaque to optimize visual colorationeffects if only gas filled the void space between primary particles, itis useful to use either a liquid or solid material in such spaces. Suchliquid or solid material can minimize undesired scattering effects dueto fissures and grain boundaries that interrupt the periodic packing ofthe primary particles. In such case, it is preferable if such fluid orsolid has a refractive index in the visible range that is within 5% ofthe primary particles.

[0095] Another method for providing useful particle scattering colorantsutilizes polymer primary particles that form an ordered array in polymerhost, which serves as a binder. Films suitable for the preparation ofsuch particle scattering colorants were made by E. A. Kamenetzky et al.as part of work that is described in Science 263, pp. 207-210 (1994).These authors formed films of three-dimensionally ordered arrays ofcolloidal polystyrene spheres by the ultraviolet-induced setting of aacrylamid-methylene-bisacrylamide gel that contained an ordered array ofsuch spheres. The size of the polymer spheres was about 0.1 microns, andthe nearest neighbor separation of the spheres was comparable to thewavelength of visible light radiation. A method for producing filmsconsisting of three-dimensionally ordered polymer primary particles thatdo not utilize a binder polymer is described by G. H. Ma and T. Fukutomiin Macromolecules 25, 1870-1875 (1992). These authors obtained suchiridescent films by casting an aqueous solution of monodispersedpoly(4-vinylpyridine) microgel particles that are either 250 or 700 nmin diameter, and then evaporating the water at 60° C. These films weremechanically stabilized by a cross-linking reaction that used either adihalobutane or p-(chloromethyl)styrene. Particle scattering colorantssuitable for the present invention embodiments can be made by cuttingeither of the above described film types so as to provide particles ofdesired dimensions. One preferred cutting method is the process used byMeadowbrook Inventions in New Jersey to make glitter particles frommetallized films. Various mechanical grinding processes might be usedfor the same purpose, although it should be recognized that lowtemperatures might be usefully employed to provide brittleness thatenables such a grinding process. For use as particle scatteringcolorants, it is preferably that the cutting or grinding process produceparticles that are of convenient dimension for incorporation withoutsubstantial damage in the host matrix, which is preferably a polymer.

[0096] The particle scattering colorants of this invention embodimentare preferably formed in required sizes during the aggregation ofprimary particles. Any methods used for post-formation reduction inparticle sizes should be sufficiently mild as to not interfere with thedesired periodicity of the primary particles. Likewise, processingconditions during commingling of the particle scattering colorant ineither the polymer matrix (or a precursor therefore) and other stepsleading to the formation of the final article should not substantiallydestroy the optical effect of the periodic assembly of primaryparticles. For particle scattering colorants that are not designed to bemechanically robust, preferred processes for mixing of particlescattering colorant and the matrix polymer (or a precursor thereof) arein a low viscosity fluid state, such as in a monomer, a prepolymer, or asolution of the polymer used for the matrix. For such polymers that arenot designed to be mechanically robust, film fabrication and articlecoating using solution deposition methods are preferred for obtainingthe particle scattering colorant dispersed in the shaped matrix polymer.Likewise, for such non-robust particle scattering colorants, polymermatrix formation in shaped form by reaction of a liquid containing theparticle scattering colorant is preferred, such as by thermalpolymerization, photopolymerization, or polymerization using otheractinic radiations. Reaction injection molding is especially preferredfor obtaining molded parts that incorporate particle scatteringcolorants that are not mechanically robust.

[0097] In another embodiment of this invention the particle scatteringcolorant consists of primary particles that are translationally periodicin two dimensions, rather than in three dimensions. Fiber-like primaryparticles having an approximately uniform cross-section orthogonal tothe fiber-axis direction tend to aggregate in this way when dispersed insuitable liquids. Likewise, spherical primary particles tend toaggregate as arrays having two-dimensional periodicity when deposited onplanar surfaces. For example, such particles can be formed on thesurface of a liquid (or a rotating drum) in a polymer binder thatadhesively binds the spherical particles into two-dimensional arrays.These array sheets can then be either cut or ground into the particlesizes that are desired for the particle scattering colorant.

[0098] For all of the above invention embodiment of particle scatteringcolorants that consist of translationally periodic primary particles, itis preferable for the volume occupied by the particle scatteringcolorants to be less than about 75% or the total volume of the matrixpolymer and the particle scattering colorant. The reason for thispreference is that the use of low loading levels of the particlescattering colorant can lead to improved mechanical properties for thecomposite, relative to those obtained at high loading levels. Asdescribed above for particle scattering colorants that are notaggregates of periodically arranged primary particles, the visual effectof the particle scattering colorants consisting of ordered arrays ofprimary particles can be enhanced using electronic transition colorants.Such means of enhancement, as well as methods for achieving color changeeffects that are switchable, are analogous to those described herein forother types of particle scattering colorants.

[0099] From a viewpoint of achieving coloration effects for polymerarticles that are easily eliminated during polymer recycling, particlescattering colorants that consist of translationally-ordered primaryparticle arrays can provide special advantages, especially if theprimary particles do not substantially absorb in the visible region andthe polymer article does not include an electronic transition colorant.The reason is that processing steps that disrupt such arrays can greatlyreduce coloration effects. From this viewpoint of polymer recycling, itis useful to provide particle scattering colorants that are convenientlydisrupted by either thermal, mechanical, or chemical steps.

[0100] Various applications for which the compositions of this inventionhave utility will be obvious to those skilled in the art. However, forsuch articles having switchable coloration or switchable transparencythat is broadband in the visible, more detailed descriptions ofapplications embodiments are provided in the following. One suchapplication is in privacy panels, windows, displays, and signs in whichthe electric-field- induced switchability of the refractive index of aparticle scattering colorant, an electronic transition colorant, or oneor more matrix components provides either device operation or anenhancement of device operation. In one example type, theelectric-field-induced-change in the refractive index difference betweenparticle scattering colorant and the surrounding matrix component can beused to change either (1) the transparency of an overcoating layer on asign (so that an underlying message is switched between visible andinvisible states) or (2) the transparency of either a privacy panel or awindow. For displays and signs, an electric field applied to a matrixlayer containing the particle scattering colorant can cause the degreeof particle scattering to change—therefore changing the effectiveviewing angle for an underlying message (such as produced by aback-lighted liquid-crystal display or other types of static orchangeable information-providing materials). The electric field canprovide switchable properties to either the particle scatteringcolorant, the matrix material for that colorant, an electronictransition colorant, or any other kind on information display material,or any combination of these materials.

[0101] Most preferably, the direction of a refractive index changeprovided by a particle scattering colorant (caused by an ambientinfluence, such as an applied electric field, temperature,time-temperature exposure, humidity, or a chemical agent) is in anopposite direction to that of the host materials. In this preferredcase, the sensitivity of particle scattering to applied electric fieldor other ambient influence is enhanced by the refractive index change ofboth the particle scattering colorant and the matrix material for thiscolorant. Most preferably, such difference in the direction ofrefractive index change for particle scattering colorant and matrixmaterial is for all possible light polarization directions. For theabove applications, electric fields can be applied in either patternedor unpatterned ways and different electric field can be applied to theparticle scattering colorant and other materials, such as the electronictransition colorant. In general the local field that is across aparticle scattering colorant in a matrix depends upon the state ofaggregation of that colorant in the matrix, so a patterned variation insuch degree of aggregation can be used to provide a patterned differencein the response of the particle scattering colorant to an appliedelectric field. For example, if the electric conductivity and thedielectric constant of the particle scattering colorant are both largerthan that of the matrix, an increased voltage drop across the particlescattering colorant can be provided by increasing the degree of particleaggregation. If the switchability in particle scattering is largely aresult of the electric field influence on the particle scatteringcolorant, such aggregation can increase the switchability.

[0102] Display or lighting devices that involve electroluminescentcompositions provide special application opportunities. For example, theelectric-field-switching of particle scattering can be used to eitherchange the degree of diffuse light scattering from electroluminescentlight source or to provide a patterned distribution of light emission.In a preferred case, particles of the electroluminescent compositionserve as a particle scattering colorant. Another application of thisinvention in the lighting area is for light bulbs and lighting fixturesthat slowly become transmissive after the light switch is pulled, whichis an application of thermochromic materials that is described in U.S.Pat. No. 5,083,251, which is incorporated herein by reference. Suchlight sources are sought after to provide natural time-dependentlighting effects reminiscent of the rising of the sun. An example ofsuch technology that uses a vanishing Δn embodiment is obtained byemploying a particle scattering colorant that at room temperature has arefractive index that is unmatched at any point in the visible with thatof the host matrix. The particle scattering colorant is selected so thatthe heating of the light source causes the refractive index or theparticle scattering colorant and the matrix to become matched in thevisible. Hence, the heating process eliminates particle scattering atthe matching wavelength, so that the light source becomes moretransmissive. If this matching is desired to be broadband, then thereshould be little dispersion of the refractive index difference betweenthe particle scattering colorant over the visible wavelength range. Insuch case where little dispersion in Δn is wanted, the particlescattering colorant and the matrix can be chosen so that the differencein n_(F)−n_(C) for the particle scattering colorant and the matrixcomponent is smaller in absolute magnitude than 0.0001. For thisapplication mode, it is most preferable if the match between therefractive index of the matrix and that of the particle scatteringcolorant is achieved discontinuously upon increasing temperature above adesired temperature as a consequence of a discontinuous phase transitionof either the particle scattering colorant or the matrix material.Otherwise, the color of the transmitted light will vary somewhatcontinuously with the temperature of the particle scattering colorantand associated matrix material.

[0103] Indicators devices for chemical agents, pressure, temperature,moisture pickup, temperature limits (such as freeze or defrostindicators), and time-temperature exposure provide other applicationsopportunities for the particle scattering colorants of this invention.For such devices, either reversibly or irreversibly switched colorationcan result as a consequence of switchability in either the refractiveindex or the electronic transitions of either particle scatteringcolorants, matrix components, or electronic transition colorants. Forthe mentioned time-temperature indicators, a color change can indicatethat either a desired thermal exposure has occurred (such as for productprocessing) or that an undesired thermal exposure has occurred (leadingto undesired degradation of a perishable product). Using the vanishingΔn embodiment, the wavelength at which a match in refractive indexoccurs between matrix and particle scattering colorant can be a functionof integrated thermal exposure. For example, polymer films that are usedfor the packaging of frozen vegetables can undergo a color change whenthe vegetables have been suitably heated for consumption. As anotherexample of the use of the vanishing Δn embodiment for indicatingsuccessful processing, a resin that is undergoing set (such as circuitboard) can contain a particle scattering colorant in the setting matrix.The changing refractive index difference between the particle scatteringcolorant and the matrix then provides a color response that indicateswhen satisfactory resin set has occurred. A similar useful example ofthe application of particle scattering coloration (in the vanishing Δnembodiment) is for the indication of moisture pickup for polymers, suchas nylon 6—so as to avoid the unsuccessful processing that would occurif the polymer has too high a moisture pickup.

[0104] Particle scattering colorants of this invention also enable theconvenient labeling of articles, such as polymer films, using thethermal or photochemical changes in refractive index or electronictransitions that occur as a result of patterned laser beam exposureduring high speed product packaging operations. For example, numberswritten by a laser on a polymer film used for packaging can becomevisible as a result of light-induced changes in the refractive indexdifference between the particle scattering colorant and the matrix. Suchswitchable particle scattering colorant/matrix combinations can also beused as a signature in order to thwart product counterfeitingactivities. The particle scattering colorants can even be used forapplications where the switchability in refractive index match atultraviolet light wavelengths provides materials operation. For example,an intelligent sunscreen for bathers can be provided by dispersing aparticle scattering colorant in a fluid matrix that is initially matchedat ultraviolet solar wavelengths with that of the particles. Alight-induced change in refractive index of either the matrix or theparticle scattering colorant (so that refractive index matching nolonger occurs) can provide an enhanced effectiveness of the sun screenas a function of increasing solar exposure.

[0105] The particle scattering colorant embodiments of the presentinvention are especially useful for the polymer articles formed bydesk-top manufacturing methods. The prior art technologies for desk topmanufacturing (which is also called rapid prototyping) are described inModern Plastics, August 1990, pp. 40-43 and in CHEMTECH, October 1990,pp. 615-619. Examples of such methods are various stereolithographytechnologies that involve either the patterned electron beampolymerization or patterned photopolymerization of monomers. In suchcase the particle scattering colorant and optional electronic transitioncolorant can be dispersed in the photomonomer-containing fluid. Inaddition to providing coloration, such materials can provide additionalbenefits of reducing shrinkage during resin cure. Vinyl ether oligomersand monomers, that are used in conjunction with triarylsulfonium salts,are especially preferred for these applications. This is theultraviolet-cured Vectomer™ system that has been developed byAlliedSignal. The particle size of the particle scattering colorant, aswell as other possible solid additives, should be sufficiently smallthat these particles do not settle appreciably during the fabrication ofan article. For this reason, particle scattering colorants that havecolloidal dimensions are particularly preferred. Another method forrapid prototyping is the Laminated Object Lamination Method in whichroll-fed sheets of polymer are cut by a soft-ware guided lightbeam—thereby building up the article one sheet at a time. In this methodthe particle scattering colorant and optional electronic colorant can beeither located in the polymer sheets, the adhesive that is used to bindthe sheets, or both. In another method used for rapid prototyping, thinlayers of a powder are deposited on the surface of the article beingconstructed, and these layers are fused in a patterned manner using alight beam. Alternatively, a binder (or a precursor thereof) is sprayedin a patterned manner on the powder (such as by using ink-jet spraying),thereby enabling article shaping in three dimensions. As anotheralternative, the powder layers can be replaced by a squeegeed gel layerthat is photoset in a patterned manner. In these methods, the particlescattering colorants and optional electronic transition colorants ofpresently described invention embodiments can be incorporated in theinitial powders, the binder, the gel polymer, or combinations thereof.Another technology for rapid prototyping builds three-dimensionalarticles by the patterned extrusion of thin coils of polymer. In suchcase, the particle scattering colorants and optional electroniccolorants of the present invention can be additives to the moltenpolymer. In any of the above described technologies for rapidprototyping, material coloration can be obtained by using either thelarge Δn embodiment or the vanishing Δn embodiment of the presentinvention.

[0106] The following specific examples are presented to moreparticularly illustrate the invention, and should not be construed asbeing limitations on the scope of the invention.

EXAMPLE 1

[0107] This example describes the achievement of blue coloration and anangle dependent hue of shade by the melt spinning of trilobal fibersfrom a mixture of a non-absorbing particle scattering colorant (which isa 35 nm average diameter titanium dioxide) and an electronic transitioncolorant in a nylon matrix polymer. The colored fiber produced in thisexample consists of a commingled mixture of both the particle scatteringcolorant (titanium dioxide) and the electronic transition colorant(carbon black) in one nylon matrix. Unless otherwise noted, the nylonused in this and following examples is MBM, a nylon 6 produced byAlliedSignal Inc. Titanium dioxide particles of MT-500B (which is anuncoated titanium dioxide from Daicolor-Pope having an average particlediameter of 35 nm) were dry-blended at a 10% by weight concentrationwith dry nylon 6. The mixture was extruded, pelletized, and redried. The10% sample was dry-blended with more nylon 6, extruded, pelletized, andredried to a final let-down concentration of 1%. A carbon blackmasterbatch produced by AlliedSignal (containing 20% carbon black innylon 6) was let-down to a 1% carbon black concentration by dry-blendingthe master batch with nylon 6, extruding, pelletizing, and redrying themixture. The 1% titanium dioxide in nylon mixture was chip-blended withthe 1% carbon black in nylon mixture at a weight ratio of 99.5/0.5,respectively. The resulting mixture was spun into fibers ofapproximately 50 μm outer diameter, drawn at a 3.2/1 draw ratio, andtexturized. The resulting fiber was a light blue to gray-blue with anangle-dependent hue in shade.

EXAMPLE 2

[0108] This example describes the modification of the Example 1 processby the use of Caplube™, which is a vegetable oil based material thatacts as a dispersing agent for the titanium dioxide particle scatteringcolorant. The carbon black concentration in the nylon composite that iscommingled with a titanium dioxide/nylon composite is an order ofmagnitude lower than for Example 1. However, the amount of the carbonblack/nylon composite that is commingled with the titanium dioxide/nyloncomposite is correspondingly increased, so that the titaniumdioxide/carbon black ratio obtained by commingling is essentiallyunchanged from that of Example 1. As a result, the fiber colorationobtained in this example is essentially the same as for Example 1.Titanium dioxide particles of MT-500B having an average diameter of 35nm were milled with Caplube overnight to a 40 weight percent paste oftitanium dioxide in Caplube. The resulting mixture was dry-blended withdry nylon 6 to yield a final concentration of titanium dioxide of 1% byweight. This mixture was then extruded, pelletized, and redried. A 0.1%by weight carbon black composite in nylon 6 was made in a similar way asdescribed in Example 1 for a 1% by weight carbon black concentration.The 1% titanium dioxide in nylon mixture was chip-blended with the 0.1%carbon black in nylon mixture at a weight ratio of 95/5, respectively.Fiber was spun, drawn and texturized from the resulting mixture usingthe process of Example 1. The resulting fiber was a light blue togray-blue with an angle-dependent hue in shade.

EXAMPLE 3

[0109] This example describes the achievement of a light blue togray-blue coloration and an angle dependent hue in shade by the meltspinning of trilobal fibers from a mixture of a non-absorbing particlescattering colorant in nylon 6 and carbon black in polypropylene. Whilethe particle scattering colorant (titanium dioxide) and the electronictransition colorant were in separate matrices, these matrices werecommingled in a substantially interpenetrating manner by a melt mixingprocess. A 1% by weight composite of the MT-500B titanium dioxide innylon was made as described in Example 1. Carbon black was dry-blended,extruded, and pelletized in polypropylene (from Himont Co.) to a finalconcentration of 0.1 weight percent. The 1% titanium dioxide in nylonmixture was chip-blended with the 0.1% carbon black in polypropylenemixture at a weight ratio of 98/2, respectively. The resulting mixturewas spun into fiber, drawn and texturized using the process ofExample 1. The resulting fiber was a light blue to gray-blue with anangle-dependent hue in shade.

EXAMPLE 4

[0110] This example demonstrates that the coloration effect can besubstantially changed if the titanium dioxide/nylon mixture is thesheath and the carbon black/nylon mixture is the core of a trilobalsheath-core fiber. This example contrasts with that of Examples 1 and 2(where the particle scattering colorant and the electronic transitioncolorant were mixed together in the nylon) and with Example 3 (where theparticle scattering colorant is mixed in nylon 6, the electronictransition colorant was mixed in polypropylene, and these two polymermixtures were then commingled together prior to the spinning process).Titanium dioxide particles of MT-500B were dry-blended at a 10% weightconcentration with nylon 6 and then let-down with additional nylon 6 toa titanium dioxide weight concentration of 5%. A 1% by weightconcentration of carbon black in nylon 6 was made as described inExample 1. The titanium dioxide nylon blend (5% titanium dioxide) andthe carbon black nylon blend (1% carbon black) were spun into a trilobalsheath-core fiber yarn containing 64 filaments per fiber bundle. Thevolumetric sheath/core ratio was 60/40 and the individual fibers had amaximum diameter of about 50 microns. The resulting fiber yarn was navyblue. The yarn was subsequently drawn at a 3.2/1 draw ratio to produce a1305 denier yarn. The drawn yarn was then texturized. The drawn andtexturized yarn was a navy blue of a very slightly darker shade than theundrawn fiber.

EXAMPLE 5

[0111] This example shows the effect of changing from a trilobalsheath/core fiber with a volumetric sheath/core ratio of 60/40 inExample 4 to a round sheath/core fiber with a volumetric sheath/coreratio of 70/30. In both this example and Example 4 the polymer matrixcontaining the particle scattering colorant is exterior to the polymermatrix containing the electronic absorption colorant. A nylon compositewith 5% by weight MT-500B titanium dioxide and a nylon composite with 1%by weight carbon black were made as described in Example 4. The 5%titanium dioxide/nylon blend and the 1% carbon black/nylon blend werespun into round sheath-core fibers that were combined to form a yarnhaving 128 filaments per fiber bundle. The carbon black phase was in thecore and the titanium dioxide in the sheath in the individual fibers,which had an outer diameter of about 50 microns. The volumetricsheath/core ratio was 70/30. The yarn was navy blue, and was a slightlylighter shade than for the yarn in Example 4. The yarn was subsequentlydrawn at a 3.2/1 draw ratio and texturized. The resulting drawn andtexturized yarn was a navy blue of a very slightly darker shade than theundrawn fiber, but of a lighter shade than the drawn and texturizedfiber yarn of Example 4.

EXAMPLE 6

[0112] This example shows the combined effect of further decrease in thevolumetric sheath/core ratio (compared with that of Examples 4 and 5), adecrease in the carbon black concentration in the core, and a decreasein the titanium dioxide concentration in the sheath. A nylon compositewith 1% by weight MT-500B titanium dioxide was made as described inExample 1. A carbon black masterbatch containing 20% carbon black innylon 6 was let-down in two steps to a 0.03% by weight carbon blackconcentration. The 1% titanium dioxide/nylon blend and the 0.03% carbonblack/nylon blend were spun into round sheath-core fibers, that werecombined to form a fiber yarn containing 144 filaments. The carbon blackcontaining nylon was in the core and the titanium dioxide containingnylon was in the sheath in individual fibers having an average outerdiameter of about 50 microns. The volumetric sheath/core ratio was 95/5.The resulting yarn was pale blue/gray. The yarn color was significantlylighter than example 4 and 5. This yarn was subsequently drawn at a3.2/1 draw ratio, resulting in a drawn yarn that is 2637 total denier.The drawn yarn was texturized and processed into sleeves and carpet. Theresulting yarn was a blue/gray and had an angle-dependent hue in shade.The shade was a very slightly grayer shade than for the undrawn yarn,but of a significantly lighter shade than the drawn and texturized yarnof Example 4.

EXAMPLE 7

[0113] This example further shows the effects of changing the titaniumdioxide concentration, the carbon black concentration, and thesheath/core ratio for sheath/core fibers. In this example the polymermatrix containing the particle scattering colorant is substantiallyexterior to the polymer matrix containing the electronic absorptioncolorant. Titanium dioxide particles of MT-500B having an averagedimension of 35 nm were dry-blended at a 10% weight concentration withnylon 6. The mixture was extruded, pelletized, and redried. The 10%sample was dry-blended with more nylon 6, extruded, pelletized, andredried to a final let-down gravimetric concentration of 6.2%. A carbonblack masterbatch containing 20% by weight carbon black in nylon 6 waslet-down to a 1.54% by weight carbon black concentration by dry-blendingthe master batch with nylon 6, extruding, pelletizing, and redrying themixture. The 6.2% titanium dioxide/nylon blend and the 1.54% carbonblack/nylon blend were spun into trilobal sheath-core fibers, and thesefibers were combined to form a yarn containing 64 filaments. The carbonblack phase was in the core and the titanium dioxide in the sheath forthe individual fibers, and the fiber outer diameter was about 50microns. The volumetric sheath/core ratio was 80/20. The resulting fiberwas blue with a light purple cast. The fiber color was lighter shadethan in Example 5. The yarn was subsequently drawn at a 3.2/1 drawratio, texturized, and processed into sleeves and carpet. The resultingarticles were medium blue.

EXAMPLE 8

[0114] This example further shows the effect of changing the carbonblack concentration and the sheath/core ratio for sheath/core fibers, ascompared with that for Examples 4 and 5. In this example the polymermatrix containing the particle scattering colorant is substantiallyexterior to the polymer matrix containing the electronic absorptioncolorant. Titanium dioxide particles of MT-500B having an averagedimension of 35 nm were dry-blended at a 10% weight concentration withnylon 6. The mixture was extruded, pelletized, and redried. The 10%sample was dry-blended with more nylon 6, extruded, pelletized, andredried to a final let-down concentration of 5% by weight titaniumdioxide. A carbon black masterbatch containing 20% carbon black in nylon6 was let-down to a 1.9% by weight carbon black concentration bydry-blending the master batch with nylon 6, extruding, pelletizing, andredrying the mixture. The 5.0% titanium dioxide/nylon blend and the 1.9%carbon black/nylon blend were spun into trilobal sheath-core fibershaving a maximum outer diameter of about 50 microns. These fibers werecombined to form a yarn containing 64 filaments that had a total denierof 3025. The carbon black phase was in the core and the titanium dioxidein the sheath. The volumetric sheath/core ratio was 65/35. The resultingyarn was a dark blue. The yarn color was lighter shade than in Example4. The yarn was subsequently drawn at a 3.2/1 draw ratio, texturized,and processed into a cut-pile carpet and woven sleeves. These articleswere a dark blue.

EXAMPLE 9

[0115] This example, which can be compared with Examples 4 and 5, showshow to obtain a very dark blue coloration. In this example the polymermatrix containing the particle scattering colorant is exterior to thepolymer matrix containing the electronic absorption colorant. Titaniumdioxide particles of MT-500B having an average dimension of 35 nm weredry-blended at a 10% weight concentration with nylon 6. The mixture wasextruded, pelletized, and redried. The 10% sample was dry-blended withmore nylon 6, extruded, pelletized, and redried to a final let-downgravimetric titanium dioxide concentration of 3.8%. A carbon blackmasterbatch containing 20% by weight carbon black in nylon 6 waslet-down to a 0.46% by weight carbon black concentration by dry-blendingthe master batch with nylon 6, extruding, pelletizing, and redrying themixture. The 3.8% titanium dioxide/nylon blend and the 0.46% carbonblack/nylon blend were spun into trilobal sheath-core fibers having amaximum exterior diameter of 50 microns. The carbon black containingnylon was in the core and the titanium dioxide containing nylon was inthe sheath for the individual fibers. These fibers were combined toprovide a yarn containing 64 filaments that had a total denier of 2064.The volumetric sheath/core ratio was 50/50 for the individual fibers andthe color of these fibers was a dark navy blue. The yarn color wasdarker than in Example 4. The fiber was subsequently drawn at a 3.2/1draw ratio, texturized, and processed into a cut-pile carpet. Thiscarpet was a dark, navy gray/blue.

EXAMPLE 10

[0116] This example shows the effect of changing the particle size ofthe titanium dioxide compared with that used for above examples that usetitanium dioxide as a particle scattering colorant, such as Example 8.In this example, although the titanium dioxide is claimed to have a“blue tone in whites and tints”, the particle size is too large forinvention embodiments, and the titanium dioxide does not satisfy thecriteria for a particle scattering colorant in high Δn embodiments. ThisTiO₂ is here shown to produce a gray fiber. Titanium dioxide 555 fromWhittaker, Clark, and Daniels, Inc. was dry-blended at a 10% weightconcentration with nylon 6. The mixture was extruded, pelletized, andredried. The 10% sample was dry-blended with more nylon 6, extruded,pelletized, and redried to a final let-down concentration of 5%. Acarbon black masterbatch containing 20% by weight carbon black in nylon6 was let-down to a 1.9% by weight carbon black concentration bydry-blending the master batch with nylon 6, extruding, pelletizing, andredrying the mixture. The 5.0% titanium dioxide/nylon blend and the 1.9%carbon black/nylon blend were spun into trilobal sheath-core fibers thathad a maximum outer diameter of about 50 microns. The carbon black phasewas in the core and the titanium dioxide was in the sheath. Thevolumetric sheath/core ratio was 65/35. A yarn was formed by combining64 such fibers. This yarn was a medium gray and did not have a bluetone. The yarn was subsequently drawn at a 3.2/1 draw ratio, texturized,and processed into a cut-pile carpet. The resulting carpet was a mediumgray. Hence, the titanium was not effective in acting as a particlescattering colorant.

EXAMPLE 11

[0117] This example supports the demonstration of Example 10 that theuse of too large a particle size for the titanium dioxide particlesprovides materials that do not have significant particle scatteringcoloration. As for Example 10, the titanium dioxide used was titaniumdioxide 555 from Whittaker, Clark, and Daniels, Inc. The differencebetween this example and Example 10 is that the trilobal carpet fibershad a sheath that was 6.2 weight percent titanium dioxide in nylon, acore that was a 1.54 weight percent carbon black in nylon, and thevolumetric sheath/core ratio before drawing was 80/20. Other than theincrease in the particle size of the titanium dioxide, all preparativedetails are the same as for Example 7. However, while the cut-pilecarpet of Example 7 was a medium blue, the carpet produced in thisexample was a light gray.

EXAMPLE 12

[0118] This example demonstrates that, by producing a yarn in whichdifferent fibers have a slightly different sheath/core ratio along theirlengths, one can produce a yarn with multiple shades without havingstreaks of color. In this example the polymer matrix containing theparticle scattering colorant is exterior to the polymer matrixcontaining the electronic absorption colorant. A nylon composite with 5%by weight MT-500B titanium dioxide and a nylon composite with 1% byweight carbon black were made as described in Example 4. The 5% titaniumdioxide/nylon blend and the 1% carbon black/nylon blend were spun intoround sheath-core fibers having diameters of about 50 microns. Thecarbon black composite was in the core and the titanium dioxidecomposite was in the sheath. The spinning pack was set-up to permitvariation in the sheath/core ratio during the spinning of individualfilaments. This variation in sheath/core ratio was achieved by varyingthe pressure generated by the pump used to provide the sheath materialstream for the filaments, while keeping constant the pressure generatedby the pump used to provide the core material stream. The averagevolumetric sheath/core ratio was 90/10, although this ratio varied alongthe fiber length according to the pressure provided by the pump for thecore material. The different sections of the resulting yarn weredifferent shades of blue, ranging from an off-white up to a navy blue.The fiber was subsequently drawn at a 3.2/1 draw ratio, and texturized.The resulting yarn was multi-colored and contained individual filamentslengths having shades from an off-white to a navy blue.

EXAMPLE 13

[0119] This example shows how one can obtain various other colors forsheath-core fibers. In this example the polymer matrix containing theparticle scattering colorant is substantially exterior to the polymermatrix containing the electronic absorption colorant. The electronicabsorption colorant in this example is a red pigment called Fire EngineRed. The Fire Engine Red nylon 6 sample was obtained from AlliedSignaland contains a red pigment from Stanridge Color Company. A 6.2% byweight composite of MT-500B titanium dioxide in nylon 6 was made asdescribed in Example 7. The 6.2% titanium dioxide/nylon blend and theFire Engine Red/nylon blend were spun into trilobal sheath-core fibershaving a volumetric sheath/core ratio of 65/35 and a maximum diameter ofabout 50 microns. These fibers were combined at the spinneret to form ayarn containing 64 filaments. This yarn was purple. The red pigmentcontaining nylon composite was in the core and the titanium dioxidecontaining nylon composite was in the sheath of individual fibers. Theyarn was subsequently drawn at a 3.2/1 draw ratio, texturized, andprocessed into sleeves. The resulting sleeves were a shade of purple.

EXAMPLE 14

[0120] This example shows that zinc oxide can be used together withcarbon black to provide a blue coloration, for nylon fibers. Thenanosized zinc oxide was obtained from Nyacol Company. Fibers wereobtained by spinning a zinc oxide/nylon composite through an apparatusthat had previously been used for the spinning of carbon black/nyloncomposite. The result was the achievement of a blue coloration for thezinc oxide/nylon fibers as a result of the pickup of the carbonblack/nylon composite that was residual in the spinning apparatus. Sixpellets of 20% by weight carbon black in nylon and six pellets of 10 ppmcarbon black in nylon were mixed together and pushed through a meltindexer, which was used as the spinning apparatus. Then three successive2-3 gram batches of 1% by weight of zinc oxide in nylon were pushedthrough the melt indexer to give a first pass, second pass, and thirdpass fiber samples. These filaments were gray with a blue cast. Thecolor of fibers from each successive pass was somewhat lighter thanthose for the previous passes.

EXAMPLE 15

[0121] This experiment demonstrates the coloration resulting from theextrusion of nylon from a mixture of a non-absorbing particle scatteringcolorant and an electronic transition colorant in a nylon matrixpolymer. The particle scattering colorant in this example was titaniumdioxide and the electronic transition colorant was iron oxide. Titaniumdioxide particles of MT-500B having an average particle dimension of 35nm were dispersed in nylon 6 to a 2% by weight blend. Iron oxide wasdry-blended with nylon 6 to a 1% by weight blend. Ten grams of the 1%iron oxide/nylon sample, 495 g of the 2% titanium dioxide mixture, and495 g of nylon 6 were dry-blended, extruded, pelletized, and redried toyield pellets with overall concentrations of 0.01% iron oxide and 0.99%titanium dioxide. The pellets were a bright, rosy pink with a lightbluish undertone.

EXAMPLE 16

[0122] This example serves as a comparison with example 15 anddemonstrates the standard effects expected for iron oxide. Iron oxidewas dry-blended with nylon 6 to a 1% by weight blend. Ten grams of the1% iron oxide/nylon sample was dry-blended with 990 g of nylon 6. Thesample was extruded, pelletized, and redried to yield pellets withoverall concentrations of 0.01% iron oxide. The pellets were a watery,dull, salmon pink.

EXAMPLE 17

[0123] This experiment serves as a comparison with Example 15 and 16 anddemonstrates the standard effects expected for iron oxide and a particlesize titanium dioxide that is not effective as a particle scatteringcolorant. For this example titanium dioxide 555 available fromWhittaker, Clark, and Daniels, Inc. was used. Note that, although thistitanium dioxide is used to produce the blue tone described in theliterature in white and tints, it is a larger particle size than theMT500-B and does not provide the novel optical effects seen in thisinvention (Example 15). Titanium dioxide particles of Whittaker 555 havea particle size such that a maximum of 0.01% is retained on a 325 meshscreen. The estimated average particle dimension is above 200 nm. TheWhittaker titanium dioxide was dispersed in nylon 6 to a 5% by weightblend. Iron oxide was dry-blended with nylon 6 to a 1% by weight blend.Ten grams of the 1% iron oxide/nylon sample, 198 g of the 5% titaniumdioxide mixture, and 792 g of nylon 6 were dry-blended, extruded,pelletized, and redried to yield pellets with overall concentrations of0.01% iron oxide and 0.99% titanium dioxide. The pellets were a soft,pale pink with no bluish undertone.

EXAMPLE 18

[0124] This experiment, which is for comparison with Example 15,demonstrates the achievement of a blue coloration for polymer pelletsformed from a mixture of a non-absorbing particle scattering colorantand an electronic transition colorant in a nylon matrix polymer (wherecarbon black serves as the electronic transition colorant and titaniumdioxide serves as the particle scattering colorant). Titanium dioxideparticles of MT-500B having an average particle dimension of 35 nm weredispersed in nylon 6 to a 2% by weight blend. Carbon black was let-downto a 1% by weight blend from a 20% by weight masterbatch in nylon 6.Nylon 6, thel % carbon black, and the 2% titanium dioxide mixture weredry-blended, extruded, pelletized, and redried to yield nylon pelletshaving overall concentrations of 0.005% carbon black and 0.25% titaniumdioxide. The pellets were a light blue with a gray cast.

EXAMPLE 19

[0125] This experiment serves as a comparison with example 18 anddemonstrates the standard effects expected for titanium dioxide andcarbon black. For this example the titanium dioxide 555 that wasobtained from Whittaker, Clark, and Daniels, Inc. was used. It is notedthat although this titanium dioxide is used to produce the blue tonedescribed in the literature in white and tints, it is a larger particlesize than the MT500-B and does not provide the novel optical effectsseen in this invention (Example 18). Titanium dioxide particles of 555from Whittaker, Clark, and Daniels, Inc. were dispersed in nylon 6 to a2% by weight blend. Carbon black was let-down to a 1% by weight blendfrom a 20% by weight masterbatch in nylon 6. Nylon 6, carbon black (1%),and the 2% titanium dioxide mixture were dry-blended, extruded,pelletized, and redried to yield pellets with overall concentrations of0.005% carbon black and 0.25% titanium dioxide. The pellets were a graywith no blue undertone.

EXAMPLE 20

[0126] This experiment demonstrates the achievement of a gray/bluemetallic-looking fiber by using a mixture of a non-absorbing particlescattering colorant (titanium dioxide) and an electronic transitioncolorant (carbon black) in a nylon matrix polymer. Titanium dioxideparticles of MT-500B having an average particle diameter of 35 nm weredispersed in nylon 6 to a 2% by weight blend. Carbon black was let-downto a 1% by weight blend from a 20% by weight masterbatch in nylon 6. Atotal of 417.5 g of 2% titanium dioxide, 83.5 g of 1% carbon black, and1503 g of nylon 6 were dry-blended, extruded, pelletized, and redried toyield pellets with overall concentrations of 0.04167% carbon black and0.4167% titanium dioxide. The pellets were a dark blue-gray. The pelletswere spun into a gray/blue metallic-looking fiber.

EXAMPLE 21

[0127] This experiment demonstrates the achievement of novel opticaleffects and coloration that are modified compared with those of Example20. These effects were again achieved using a mixture of titaniumdioxide and carbon black in nylon. The titanium dioxide is anon-absorbing particle scattering colorant and graphite is theelectronic transition colorant. Titanium dioxide particles of MT-500Bhaving an average particle diameter of 35 nm were dispersed in nylon 6to a 2% by weight blend. Carbon black was let-down to a 1% by weightblend from a 20% by weight masterbatch in nylon 6. A total of 208.75 gof 2% titanium dioxide, 41.75 g of 1% carbon black, and 1753.5 g ofnylon 6 were dry-blended, extruded, pelletized, and redried to yieldpellets with overall concentrations of 0.0208% carbon black and 0.208%titanium oxide. The pellets were a dark blue with gray undertones. Thepellets were spun into fibers producing a gray-blue metallic-lookingfiber of slightly brighter metallic color than Example 20.

EXAMPLE 22

[0128] This example is to illustrate the effects obtainable for anabsorbing particle scattering colorant. In this example gold particleswere used to confer a pink coloration to nylon. A gold colloid solutionwas prepared by heating 95 ml of an aqueous gold chloride (III) solutioncontaining 5 mg of gold. When this solution reached the boiling point, 5ml of an aqueous 1% sodium citrate solution was added with rapidstirring. No color was visible at first. The scattering centers formedover a five-minute period. In this period the solution changed from agrayish-blue to a red. Five ml of this solution was added to 5 g offinely ground nylon and the mixture was heated in a 100° C. vacuum ovenovernight to drive off the water. The result was a pink nylon sample.This sample was extruded into fiber filaments that evidenced a pinkcoloration with some purplish-pink spots.

EXAMPLE 23

[0129] This example is for contrast with Example 22, and it shows thatthe colloidal scattering colorant should be trapped in the nylon (ratherthan aggregated on the surface) in order to obtain the desiredcoloration effect for nylon. A red colored gold colloid solution wasprepared as described in Example 22. This solution was added to an equalamount of millimeter size nylon pellets and the mixture was heated to100° C. The water boiled off, leaving only gray pellets of nylon.

EXAMPLE 24

[0130] Similar in technique to Example 22, this example demonstratesthat colloidal metals can be used to produce color in nylon 6. A goldcolloid solution was prepared by first heating 237.5 ml of an aqueousgold trichloride solution (containing 0.005% gold) to boiling. Then 12.5ml of a 1% aqueous trisodium citrate solution was added to the boilinggold trichloride solution during rapid stirring. Over 30 minutes, as thesolution boiled, the color changed from very pale grayish blue to a verydeep red. Upon cooling, all 250 ml of this deep red colloidal goldsolution was added to 500 g of finely ground nylon 6 and thoroughlymixed to produce an even color dispersion. All of the water in thismixture was then evaporated by drying the mixture overnight in a vacuumoven at 110° C. The resulting intensely pink powder containedapproximately 0.0025% colloidal gold. This powder was then spun intopink fibers containing 12 filaments per fiber bundle. The fibers weredrawn at a 3:1 draw ratio to produce pale pink drawn fibers.

EXAMPLE 25

[0131] This example demonstrates the generation of particle scatteringcolorants during extrusion using metal salts. No trisodium citrate orcomparable non-polymeric reducing agent was added. 0.104 g of an aqueous5% solution (by weight) of AgNO₃ was diluted with 10 ml deionized water.The mixture was added to 30 g of ground nylon 6. The sample was mixed,placed into a vacuum oven, and held at 85° C. for 3.5 hours. Thetemperature was raised to 100-105° C. for two hours. The resulting whiteor off white powder was removed from the oven. This powder was then spunthrough a melt indexer to yield a bright yellow filament.

EXAMPLE 26

[0132] This example further illustrates the use of metal salts toproduce color in nylon. AuCl₃ (0.015 g) was dissolved in 3.75 ml ofdeionized water. Nylon 6 (7.5 g) was added and the mixture was blended,placed in a vacuum oven and held at 85° C. for 3.5 hours. Thetemperature was raised to 100-105° C. for two hours. The resulting lightpink powder was removed from the oven. The powder was then spun througha melt indexer to yield a deep crimson filament.

EXAMPLE 27

[0133] This example demonstrates that hollow white polymer fiberscontaining titanium dioxide particle scattering colorants become blue inappearance when these fibers are fluid filled with an electronictransition colorant. Titanium dioxide particles having an averagediameter of 35 nm were dry-blended with dry MBM nylon 6 to obtain a 6.2%loading level of the titanium dioxide in the nylon. The mixture wasextruded, pelletized, and redried. The samples were spun into hollowwhite fibers that were then cut into staple. The fiber was put into awater solution containing negrosin black. The black solution entered thefiber ends through capillary action, thereby producing a blue fiber.

EXAMPLE 28

[0134] This example evidences the extraordinarily high fade resistanceof the carpets and fibers produced using particle scattering colorants.The carpets and fibers from Examples 7 and 8, as well as commerciallyavailable pigmented nylon fibers (AlliedSignal) and commerciallyavailable dyed carpet (AlliedSignal) of similar colors, were put intoundiluted household bleach solutions (a 5.25% sodium hypochloriteaqueous solution) for 72 hours. The carpets and fibers from Examples 7and 8 evidenced no fading. On the other hand, the fibers and carpetsthat were either dyed or pigmented using conventional technology allfaded, such fading being most severe for the dyed fibers and carpets.

EXAMPLE 29

[0135] This example evidences the high fade resistance to ozone exposureof woven articles (sleeves) produced using particle scatteringcolorants. Sleeves from Examples 7 and 8, as well as sleeves made fromcommercially available pigmented nylon fibers (AlliedSignal) andcommercially available dyed fibers (AlliedSignal) of similar colors,were put under a standard ozone test. The sleeves from Examples 7 and 8had no visible fading. Quite different results were obtained for thearticles made by conventional technologies for producing coloration: thefibers from the sleeves of pigmented fibers had slight fading and thesleeves from dyed fibers had substantial fading.

EXAMPLE 30

[0136] This example shows that similar coloration effects as obtained inExample 8 result when the nylon fiber sheath in this example is replacedwith either a derivatized polypropylene sheath or a polyethyleneterephthalate sheath. Both in this example and in Example 8, theparticle scattering colorant in the fiber sheath was titanium dioxideparticles of MT-500B having an average diameter of 35 nm. Also, in allof these cases the fiber core was a carbon-black/nylon composite. Thischange in the sheath polymer did not appreciably change fibercoloration, which was dark blue.

EXAMPLE 31

[0137] This experiment demonstrates the method employed for determiningwhether or not a candidate material has the properties required for useas a particle scattering colorant for high Δn embodiments of thisinvention. A 0.001% by weight dispersion of the candidate particlescattering colorant was prepared in ethylene glycol. The transmittanceof the dispersion was measured from 380 to 750 nm using a Perkin ElmerLambda 7 UV/Visible spectrophotometer, and the absorbance was calculatedfrom this transmittance. The minimum absorbance (A_(min)) and maximumabsorbance (A_(max)) were identified in the visible wavelength rangebetween 380 and 750 nm. The required ratio was then calculated as theeffective absorbance at the absorbance maximum divided by the effectiveabsorbance at the absorbance minimum. The obtained results are listedbelow. Particle Scattering A_(max)/A_(min) Material Colorant 3.06MT-500B titanium dioxide (Daicolor-Pope) Yes 1.26 Standard particletitanium dioxide (1 um, No Aldrich) 9.0 Colloidal silica (NissanChemical Yes Industries, Ltd) 3.55 UV Titan P580 titanium dioxide(Kemira) Yes 4.52 Tin oxide (5% solution, Nyacol, The PQ Corp) Yes 18.14Zirconia (10% solution, 100 nm size, Nyacol, Yes The PQ Corp) 1.55Titanium Dioxide 555 (Whittaker, No Clark and Daniels) 3.31 MT-500 HDCoated Titanium dioxide Yes (Diacolor-Pope)

[0138] All of the above particulate materials are substantiallynon-absorbing in the visible. According to whether or notA_(max)/A_(min) is above or below 2, the investigated material is aparticle scattering colorant for high Δn embodiments of this invention.With increasing values of this ratio above 2, the effectiveness of theparticle scattering colorant for producing coloration is generallyincreased.

EXAMPLE 32

[0139] This example evidences the high fade resistance to light exposureof woven articles (sleeves) produced using particle scatteringcolorants. Sleeves from Example 8 and 29 were exposed to a severe testof lightfastness: GM 112 KJ for 3 days. The sleeves had excellentlightfastness (delta ε) ratings of 0.87 for the nylon/nylon sleeve and0.79 for the PET/nylon sleeve. No fading was observed for the PET/nylonsleeve.

EXAMPLE 33

[0140] This example evidences the high bleach resistance of the colorgenerated using particle scattering colorants. Fibers from example 23were put into an undiluted solution of household bleach (a 5.25% sodiumhypochlorite aqueous solution). There was no color fading evident after96 hours exposure to bleach solution.

1. A composition comprising: (a) a polymer matrix component that issubstantially non-absorbing in the visible region of the electromagneticspectrum and having dispersed therein: (i) particle scattering colorantparticles; and (ii)at least one luminescent substance; wherein saidparticle scattering colorant particles: (1) are selected from the groupconsisting of a semiconductor, metallic conductor, metal oxide or metalsalt; (2) have an average diameter in the smallest dimension of lessthan about 0.1 micron; (3) have a minimum in the transmitted lightintensity ratio in the 380 to 750 nanometer range that is shifted atleast by 10 nanometers compared with that obtained for the samesemiconductor, metallic conductor, metal oxide or metal salt having anaverage particle size above about 20 microns; and wherein saidluminescent substance further comprises at least one fluorescentsubstance, at least one phosphorescent substance or at least onefluorescent and at least one phosphorescent substance.
 2. A compositioncomprising at least one first composition and at least one secondcomposition, and a luminescent substance dispersed within at least oneof said first and said second compositions, said first compositioncomprising a solid first matrix component in which there is dispersed anon-liquid particle scattering colorant and, said second compositioncomprising a solid second matrix component in which there is dispersedan electronic transition colorant, dye or pigment; said first and secondcompositions being located relative to one another such that said firstcomposition is either disposed on and substantially exterior to saidsecond composition on at least a part thereof or said first and secondcompositions are substantially mutually interpenetrating; wherein: (a)there exists at least one incident visible light wavelength and oneincident light angle such that said first composition absorbs less thanabout 90% of light incident on said first composition; (b) theabsorption coefficient of said first composition is less than about 50%of that of said second composition at a wavelength in the visible regionof the spectrum; (c) the highest absorption peak of the particlescattering colorant does not fall in the visible region of the spectrum;(d) either (i) said particle scattering colorant has a refractive indexthat matches that of said first matrix component at a wavelength in thevisible region of the electromagnetic spectrum and has an averageparticle size of less than about 2000 microns, or (ii) the averagerefractive index of said particle scattering colorant differs from thatof said first matrix component by at least about 5% in the visibleregion of the spectrum, the average particle size of said particlescattering colorant in the smallest dimension is less than about 2microns, and said particle scattering colorant, when dispersed in acolorless, isotropic liquid having a substantially different refractiveindex, is characterized at wavelengths in the visible region of thespectrum as having an effective maximum absorbance that is at leastabout 2 times its effective minimum absorbance; and (e) said luminescentsubstance comprises at least one fluorescent substance or at least onephosphorescent substance or at least one fluorescent and at least onephosphorescent substance.
 3. The composition of claim 1 wherein saidparticle scattering colorant particles comprise a metallic conductorselected from the group consisting of gold, platinum, copper, aluminum,lead, palladium, silver, rhodium, osmium, iridium, and alloys thereof;said particle scattering colorant particles have an average diameter inthe smallest dimension of less than about 0.2 microns; said polymermatrix component is substantially non-absorbing in the visible region ofthe spectrum; and said particle scattering colorant has a minimum in thetransmitted light intensity ratio in the 380 to 750 nanometer range thatis shifted at least by 10 nanometers compared with that obtained for thesame metallic conductor having an average particle size above about 20microns.
 4. The composition of claim 3 wherein said particle scatteringcolorant particles comprise colloidal particles.
 5. The composition ofclaim 4 wherein the transmitted light intensity ratio of said particlescattering colorant has two minima in the visible wavelength region ofthe electromagnetic spectrum and the particle size distribution of saidparticle scattering colorant approaches a mononodal distribution.
 6. Thecomposition of claim 2 wherein said at least one first compositioneither absorbs or scatters more than about 50% of uniform radiation atthe ultraviolet wavelength at which said at least one second compositionundergoes the maximum rate of color fading.
 7. The composition of claim2 wherein said particle scattering colorant is substantiallynon-absorbing in the visible region of the electromagnetic spectrum. 8.The composition of claim 2 wherein the refractive index of said particlescattering colorant is substantially different than that of said firstmatrix component at all wavelengths in the visible region of theelectromagnetic spectrum and wherein at least about 50% of all particlesof said particle scattering colorant have a smallest dimension that isless than about 0.25 microns.
 9. The composition of claim 2, wherein forsaid particle scattering colorant: (a) the average particle size is fromabout 0.001 to about 0.4 microns; (b) the average ratio of maximumdimension to minimum dimension for individual particles is less thanabout four; and (c) the refractive index is substantially different thanthat of the matrix at all wavelengths in the visible region of theelectromagnetic spectrum.
 10. The composition of claim 2 wherein: (a)the average particle size of said particle scattering colorant is lessthan about 1000 microns; (b) both said first matrix component and saidparticle scattering colorant are substantially optically isotropic; (c)there exists a wavelength in the visible region of the electromagneticspectrum at which the refractive index of said first matrix componentsubstantially equals that of said particle scattering colorant; (d) therefractive index difference of said first matrix component and saidparticle scattering colorant is substantially dependent on wavelength inthe visible range of the electromagnetic spectrum; and (e) said firstmatrix composition is substantially non-absorbing at wavelengths in thevisible region of the electromagnetic spectrum.
 11. The composition ofclaim 10 wherein said particle scattering colorant and said first matrixcomponent each exhibit refractive indices n_(F) and n_(C), at 486.1 nmand 656.3 nm respectively, and wherein the difference in n_(F)−n_(C) forsaid particle scattering colorant and said first matrix component isgreater in absolute magnitude than 0.001.
 12. The composition of claim 2wherein said first and second matrix components comprise organicpolymers.
 13. The composition of claim 1 or claim 2 wherein said matrixcomponent of claim 1 and at least one of said first and second matrixcomponents of claim 2 comprises at least one material selected from thegroup consisting of homopolymers and copolymers of polyamide, polyester,polyolefin, polyvinyl, acrylic, polysulfone, polycarbonate, polyarylateand polystyrene.
 14. The composition of claim 2 wherein said firstmatrix component and said second matrix component are substantiallymutually interpenetrating and wherein there exists a valueα_(e)v_(e)V_(e) for said second composition and α_(s)v_(s)V_(s) for saidfirst composition differ by less than a factor of ten at a wavelength inthe visible region of the electromagnetic spectrum; wherein α_(e) is theabsorption coefficient for said electronic transition colorant; α_(s) isthe effective absorption coefficient for said particle scatteringcolorant; v_(s) and v_(e) are, respectively, the volumes of said atleast one first and second compositions; and V_(s) and V_(e) arerespectively the volume fraction of said at least one first compositionthat is said particle scattering colorant and the volume fraction ofsaid at least one second composition that is said electronic transitioncolorant.
 15. An article comprising the composition of claim 2 whereinsaid at least one first composition comprises a layer disposed on and issubstantially exterior to a layer of said second matrix composition onat least one side of said article; said at least one second compositioncomprises an electronic transition colorant or a pigment; there exists awavelength of visible light and a light incidence angle at which fromabout 10% to about 90% light transmission occurs through said at leastone first composition; and there is a value for said at least one secondcomposition calculated as α_(e)t_(e)V_(e) that is greater than 0.1;wherein α_(e) is the absorption coefficient at the wavelength in thevisible region of the electromagnetic spectrum at which the maximumabsorption occurs for said electronic transition colorant or saidpigment; t_(e) is a maximum thickness of said layer comprising said atleast one second composition; and V_(e) is the volume fraction of saidat least one second composition comprising said electronic transitioncolorant or pigment.
 16. An article comprising the composition of claim1 or claim 2 wherein said article comprises at least one filament, atleast one fiber or at least one filament and at least one fiber.
 17. Thearticle of claim 16 wherein said at least one first composition forms afiber sheath that substantially covers a core that comprises said secondmatrix component.
 18. The article of claim 17 wherein said sheath andsaid core have differing cross-sectional shapes.
 19. The article ofclaim 18 in which the maximum ratio of orthogonal axial dimensions incross-section for an outer surface of said sheath is less than aboutone-half of the corresponding ratio for said core.
 20. The article ofclaim 17 where said sheath and said core both have a maximum ratio oforthogonal axial dimensions in cross-section that exceeds two and thelong axis directions in cross-section of said sheath and said core areunaligned.
 21. The article according to claim 17 comprising a pluralityof said fibers and sheaths and exhibiting spatially dependent colorationor coloration a result of size and shape variations in the cross-sectionof said sheath or the cross-section of said core.
 22. An articlecomprising the composition of claim 2 in which said particle scatteringcolorant in said at least one first composition comprises an inorganiccomposition.
 23. The article of claim 22 wherein said inorganiccomposition comprises at least one material selected from the groupconsisting of bismuth oxychloride, titanium dioxide, antimony trioxide,barium titanate, solid solutions of BaTiO₃ with SrTiO₃, PbTiO₃, BaSnO₃,CaTiO₃, or BaZrO₃, potassium lithium niobate, aluminum hydroxide,zirconium oxide, colloidal silica, lithium niobate, lithium tantalite,proustite; zinc oxide, alpha-zinc sulfide, and beta-zinc sulfide.
 24. Anarticle comprising the composition of claim 1 or claim 2 wherein saidparticle scattering colorant comprises a ferroelectric,antiferroelectric, or photoferroelectric material.
 25. An articlecomprising the composition of claim 1 wherein said article is in theform of a film or plate in which a layer of said at least one firstcomposition is joined to either one side or to both opposite sides ofsaid at least one second composition.
 26. An article comprising thecomposition of claim 2 wherein said article is in the form of a film orplate comprising at least one layer of each of said first compositionand said second composition, provided that at least one layer of saidfirst composition is present as a top or outer layer of said film orplate.
 27. The article of claim 25 or claim 26 in the form of a lightsource, visual display, sign, or switchable screen, and comprising aparticle scattering colorant, an electronic transition colorant, or amatrix that is switchable in either refractive index or absorptioncoefficient.
 28. The article of claim 26 wherein in the composition ofclaim 2 said first matrix component and said second matrix componentboth comprise an organic polymer.
 29. The article of claim 26 wherein inthe composition of claim 2 said solid first matrix component comprises apolymer matrix, and the refractive index difference between said polymermatrix and either said particle scattering colorant or said electronictransition colorant undergoes substantial change at a wavelength in thevisible spectra as a result of one or more of a temperature change,humidity change, an electric field, integrated thermal exposure, orexposure to either light or actinic radiation.
 30. The article of claim29 wherein said electronic transition colorant contains a photochromicanil, fulgide, or spiropyran.
 31. The composition of claim 2 comprisingeither an electronic transition colorant or a matrix polymer thatdisplays electronic transition coloration, wherein dichroism in thevisible range of the electromagnetic spectrum results from eitherpreferential orientation of said electronic transition colorant or saidmatrix polymer.
 32. The article of claim 16 wherein the effectivediameter of said filament is in the range of from about 0.01 to 3 mm.33. The composition of claim 1 or claim 2 wherein at least oneluminescent response is produced by a wavelength in the infrared regionof the electromagnetic spectrum.
 34. The composition of claim 1 or claim2 wherein at least one luminescent response is produced by a wavelengthin the visible region of the electromagnetic spectrum.
 35. Thecomposition of claim 1 or claim 2 wherein at least one luminescentresponse is produced by a wavelength in the ultraviolet region of theelectromagnetic spectrum.
 36. The composition of claim 1 or claim 2wherein luminescent responses are produced by at least two excitationwavelengths selected from different members of the group consisting ofthe infrared, visible, and ultraviolet region of the electromagneticspectrum.
 37. The composition of claim 2 in which saidparticle-scattering colorant comprises a gas.
 38. The composition ofclaim 37 wherein said gas is air.
 39. The composition of claim 1 orclaim 2, wherein said particle scattering colorant has an averageparticle size of less than 3 microns and comprises a plurality oflayers, each of said layers having a different refractive index.
 40. Theparticle of claim 39 wherein the refractive index difference is greaterthan about 5%.
 41. The composition of claim 1 or claim 2 comprising atleast one each of a fluorescent and a phosphorescent material.
 42. Thecomposition of claim 2 wherein said luminescent substance is dispersedin said first composition, said second composition or both.
 43. Thecomposition of claim 42 wherein said luminescent substance is dispersedin said first composition.
 44. The composition of claim 42 wherein saidluminescent substance is dispersed in said second composition.
 45. Thecomposition of claim 1 or claim 2 wherein said fluorescent orphosphorescent material is represented by the formula Zn_(1−x)Cd_(x)S,wherein x is greater than zero and no greater than unity, saidfluorescent or phosphorescent material further comprising at least onetrace element selected from the group consisting of Cu, Ag, or Mn.